Skip to content

mathematics practice

Overview

This page contains 25 practice problems organised by the four content domains of the SAT Mathematics section. Each problem includes a step-by-step solution, the key concept tested, and common mistakes to avoid. These problems span the difficulty range you will encounter on the digital SAT, from straightforward applications to multi-step problems requiring careful reasoning.


Algebra

Problem 1: Linear Equations

If 3(2x5)=4(x+3)73(2x - 5) = 4(x + 3) - 7, what is the value of xx?

Solution:

3(2x5)=4(x+3)73(2x - 5) = 4(x + 3) - 7

6x15=4x+1276x - 15 = 4x + 12 - 7

6x15=4x+56x - 15 = 4x + 5

6x4x=5+156x - 4x = 5 + 15

2x=202x = 20

x=10x = 10

Key concept: Solving a linear equation by distributing, combining like terms, and isolating the variable.

Common mistakes:

  • Forgetting to distribute the 3 to both terms in (2x5)(2x - 5)
  • Dropping the negative sign when moving 15-15 to the right side
  • Arithmetic errors in 127=512 - 7 = 5

Problem 2: Systems of Equations

A store sells notebooks for $3 each and pens for $2 each. If a customer buys 14 items and spends $34 in total, how many notebooks did the customer buy?

Solution:

Let nn = number of notebooks and pp = number of pens.

n+p=14(total items)n + p = 14 \quad \text{(total items)}

3n+2p=34(total cost)3n + 2p = 34 \quad \text{(total cost)}

From the first equation: p=14np = 14 - n.

Substitute into the second:

3n+2(14n)=343n + 2(14 - n) = 34

3n+282n=343n + 28 - 2n = 34

n+28=34n + 28 = 34

n=6n = 6

The customer bought 6 notebooks.

Key concept: Solving a system of linear equations using substitution.

Common mistakes:

  • Setting up the equations with incorrect coefficients (confusing which item costs $3 and which costs $2)
  • Solving for nn but answering with pp instead
  • Forgetting to verify: 6×3+8×2=18+16=346 \times 3 + 8 \times 2 = 18 + 16 = 34

Problem 3: Linear Functions

A line passes through the points (2,5)(-2, 5) and (4,7)(4, -7). What is the equation of this line in slope-intercept form?

Solution:

m=754(2)=126=2m = \frac{-7 - 5}{4 - (-2)} = \frac{-12}{6} = -2

Using point-slope form with point (4,7)(4, -7):

y(7)=2(x4)y - (-7) = -2(x - 4)

y+7=2x+8y + 7 = -2x + 8

y=2x+1y = -2x + 1

The equation is y=2x+1y = -2x + 1.

Key concept: Calculating slope from two points and writing the equation in slope-intercept form.

Common mistakes:

  • Reversing the order of subtraction in the slope formula (getting m=5(7)24m = \frac{5-(-7)}{-2-4} gives the same result, but inconsistent order can lead to sign errors)
  • Making arithmetic errors when substituting into point-slope form
  • Forgetting to simplify the final equation

Problem 4: Inequalities

Solve the inequality 3(2x+1)>4x11-3(2x + 1) > 4x - 11. Express the solution as an inequality.

Solution:

3(2x+1)>4x11-3(2x + 1) > 4x - 11

6x3>4x11-6x - 3 > 4x - 11

6x4x>11+3-6x - 4x > -11 + 3

10x>8-10x > -8

Dividing by 10-10 (reverse the inequality sign):

x<45x < \frac{4}{5}

Key concept: Solving a linear inequality, remembering to reverse the inequality sign when dividing by a negative number.

Common mistakes:

  • Forgetting to reverse the inequality sign when dividing by 10-10
  • Sign errors when distributing 3-3 to both terms
  • Writing 810\frac{-8}{-10} incorrectly (it simplifies to 45\frac{4}{5}, not 45-\frac{4}{5})

Problem 5: Absolute Value

What is the sum of all integer solutions to 2x37|2x - 3| \leq 7?

Solution:

2x37    72x37|2x - 3| \leq 7 \implies -7 \leq 2x - 3 \leq 7

Add 3:

42x10-4 \leq 2x \leq 10

Divide by 2:

2x5-2 \leq x \leq 5

The integer solutions are 2,1,0,1,2,3,4,5-2, -1, 0, 1, 2, 3, 4, 5.

Sum: 2+(1)+0+1+2+3+4+5=12-2 + (-1) + 0 + 1 + 2 + 3 + 4 + 5 = 12

Key concept: Solving an absolute value inequality by rewriting as a compound inequality.

Common mistakes:

  • Writing 2x372x - 3 \leq 7 only (forgetting the negative case)
  • Incorrectly dividing: dividing by a positive number (2) does not require reversing the inequality
  • Off-by-one errors when listing integer solutions (including 6 or excluding 2-2)

Problem 6: Linear Word Problem

A tank initially contains 200 litres of water. Water is added at a constant rate of 15 litres per minute. At the same time, water drains from a leak at a constant rate of 3 litres per minute. How many minutes will it take for the tank to contain 380 litres?

Solution:

Net rate of change: 153=1215 - 3 = 12 litres per minute.

Amount needed: 380200=180380 - 200 = 180 litres.

12t=18012t = 180

t=18012=15t = \frac{180}{12} = 15

It takes 15 minutes.

Key concept: Modelling a real-world scenario with a linear equation using rate of change.

Common mistakes:

  • Forgetting to account for the leak (using 15 litres/min instead of the net 12 litres/min)
  • Using the initial amount instead of the difference (380200380 - 200)
  • Arithmetic errors in 180÷12180 \div 12

Advanced Math

Problem 7: Quadratic Equations

What are the solutions to 2x25x3=02x^2 - 5x - 3 = 0?

Solution:

Factor: find two numbers that multiply to 2×(3)=62 \times (-3) = -6 and add to 5-5.

The numbers are 6-6 and 11.

2x26x+x3=02x^2 - 6x + x - 3 = 0

2x(x3)+1(x3)=02x(x - 3) + 1(x - 3) = 0

(2x+1)(x3)=0(2x + 1)(x - 3) = 0

2x+1=0    x=122x + 1 = 0 \implies x = -\frac{1}{2}

x3=0    x=3x - 3 = 0 \implies x = 3

The solutions are x=12x = -\frac{1}{2} and x=3x = 3.

Key concept: Factoring a quadratic by splitting the middle term (AC method).

Common mistakes:

  • Incorrect factor pair (e.g., 2-2 and 33 multiply to 6-6 but add to 11, not 5-5)
  • Sign errors during grouping
  • Forgetting that 2x+1=02x + 1 = 0 gives x=1/2x = -1/2, not x=1/2x = 1/2

Problem 8: Polynomial Operations

If f(x)=x3+2x25x+1f(x) = x^3 + 2x^2 - 5x + 1 and g(x)=x3g(x) = x - 3, what is the remainder when f(x)f(x) is divided by g(x)g(x)?

Solution:

By the Remainder Theorem, the remainder is f(3)f(3):

f(3)=33+2(3)25(3)+1f(3) = 3^3 + 2(3)^2 - 5(3) + 1

f(3)=27+2(9)15+1f(3) = 27 + 2(9) - 15 + 1

f(3)=27+1815+1f(3) = 27 + 18 - 15 + 1

f(3)=31f(3) = 31

The remainder is 31.

Key concept: The Remainder Theorem — the remainder of P(x)÷(xc)P(x) \div (x - c) equals P(c)P(c).

Common mistakes:

  • Evaluating f(3)f(-3) instead of f(3)f(3) (the theorem applies to xcx - c, so c=3c = 3, not 3-3)
  • Arithmetic errors in computing 333^3 or 2×92 \times 9
  • Attempting full polynomial long division (correct but slower and more error-prone)

Problem 9: Exponential Functions

A population of bacteria doubles every 3 hours. If the initial population is 500, which expression gives the population after tt hours?

A) 5002t500 \cdot 2t

B) 50023t500 \cdot 2^{3t}

C) 5002t/3500 \cdot 2^{t/3}

D) 5003t/2500 \cdot 3^{t/2}

Solution:

The population doubles every 3 hours. After tt hours, the number of doubling periods is t3\frac{t}{3}.

P(t)=5002t/3P(t) = 500 \cdot 2^{t/3}

Correct answer: C

Key concept: Writing exponential growth functions from a doubling time.

Common mistakes:

  • Choosing A, which is linear growth, not exponential
  • Choosing B, which confuses the exponent (doubling 3 times per period instead of once every 3 hours)
  • Choosing D, which swaps the base and the exponent coefficient

Problem 10: Function Composition

If f(x)=2x+1f(x) = 2x + 1 and g(x)=x23g(x) = x^2 - 3, what is f(g(4))f(g(4))?

Solution:

First evaluate g(4)g(4):

g(4)=423=163=13g(4) = 4^2 - 3 = 16 - 3 = 13

Then evaluate ff at this result:

f(13)=2(13)+1=26+1=27f(13) = 2(13) + 1 = 26 + 1 = 27

f(g(4))=27f(g(4)) = 27

Key concept: Function composition — evaluating the inner function first, then using its output as the input to the outer function.

Common mistakes:

  • Evaluating f(4)f(4) first instead of g(4)g(4) (computing g(f(4))g(f(4)) instead of f(g(4))f(g(4)))
  • Arithmetic errors: 42=164^2 = 16, not 88
  • Forgetting to apply ff to the result of g(4)g(4)

Problem 11: Nonlinear Equations

If x2+y2=25x^2 + y^2 = 25 and x+y=7x + y = 7, what is the value of xyxy?

Solution:

From x+y=7x + y = 7, square both sides:

(x+y)2=x2+2xy+y2=49(x + y)^2 = x^2 + 2xy + y^2 = 49

Substitute x2+y2=25x^2 + y^2 = 25:

25+2xy=4925 + 2xy = 49

2xy=242xy = 24

xy=12xy = 12

Key concept: Using the identity (x+y)2=x2+2xy+y2(x + y)^2 = x^2 + 2xy + y^2 to solve a system of equations without finding xx and yy individually.

Common mistakes:

  • Attempting to solve for xx and yy individually (possible but more time-consuming)
  • Forgetting the middle term 2xy2xy when expanding (x+y)2(x + y)^2
  • Dividing 24 by 2 incorrectly

Problem 12: Rational Equations

If x+13+x25=2\frac{x+1}{3} + \frac{x-2}{5} = 2, what is the value of xx?

Solution:

Multiply through by the common denominator, 15:

15x+13+15x25=15215 \cdot \frac{x+1}{3} + 15 \cdot \frac{x-2}{5} = 15 \cdot 2

5(x+1)+3(x2)=305(x + 1) + 3(x - 2) = 30

5x+5+3x6=305x + 5 + 3x - 6 = 30

8x1=308x - 1 = 30

8x=318x = 31

x=318x = \frac{31}{8}

Key concept: Solving a rational equation by clearing denominators.

Common mistakes:

  • Incorrect common denominator (the LCD of 3 and 5 is 15)
  • Sign errors when distributing: 3(x2)=3x63(x - 2) = 3x - 6, not 3x+63x + 6
  • Arithmetic errors in 5+(6)=15 + (-6) = -1

Problem 13: Quadratic in Vertex Form

The function f(x)=x28x+3f(x) = x^2 - 8x + 3 is rewritten in the form f(x)=(xh)2+kf(x) = (x - h)^2 + k. What is the value of h+kh + k?

Solution:

Complete the square:

f(x)=x28x+3=(x28x+16)16+3=(x4)213f(x) = x^2 - 8x + 3 = (x^2 - 8x + 16) - 16 + 3 = (x - 4)^2 - 13

So h=4h = 4 and k=13k = -13.

h+k=4+(13)=9h + k = 4 + (-13) = -9

Key concept: Converting a quadratic from standard form to vertex form by completing the square.

Common mistakes:

  • Incorrectly completing the square: (x4)2=x28x+16(x - 4)^2 = x^2 - 8x + 16, so you must subtract 16 to keep the expression equivalent
  • Finding hh and kk correctly but making a sign error in the sum
  • Using h=8h = 8 instead of h=4h = 4 (forgetting that the vertex form is (xh)2(x - h)^2, so hh is half of 88)

Problem Solving and Data Analysis

Problem 14: Ratios and Percentages

A shirt originally priced at $80 is discounted by 25%. An additional 10% discount is then applied to the sale price. What is the final price of the shirt?

Solution:

After the first discount:

80×(10.25)=80×0.75=6080 \times (1 - 0.25) = 80 \times 0.75 = 60

After the second discount:

60×(10.10)=60×0.90=5460 \times (1 - 0.10) = 60 \times 0.90 = 54

The final price is $54.

Key concept: Successive percentage changes multiply rather than add.

Common mistakes:

  • Adding the percentages: 25%+10%=35%25\% + 10\% = 35\% and computing 80×0.65=5280 \times 0.65 = 52 (incorrect)
  • Applying the second discount to the original price: 80×0.10=880 \times 0.10 = 8 and subtracting from $60 to get $52 (still wrong — successive discounts multiply)
  • Correct approach: each discount applies to the current price, not the original

Problem 15: Unit Conversions

A car’s fuel efficiency is 12 kilometres per litre. If petrol costs $1.45 per litre, what is the approximate cost per kilometre to drive this car? (Round to the nearest cent.)

Solution:

Cost per kilometre = (cost per litre) ÷ (kilometres per litre)

1.45120.1208\frac{1.45}{12} \approx 0.1208

Rounded to the nearest cent: approximately $0.12 per kilometre.

Key concept: Using unit rates and dimensional analysis to convert between related quantities.

Common mistakes:

  • Multiplying instead of dividing (getting $17.40 per kilometre, which is clearly unreasonable)
  • Incorrect rounding (0.1208 rounds to 0.12, not 0.13)
  • Forgetting to divide by 12 (using $1.45 per kilometre)

Problem 16: Scatter Plots and Line of Best Fit

A set of data has a least-squares regression line y^=3.2x+1.5\hat{y} = 3.2x + 1.5, where xx represents years of experience and y^\hat{y} represents predicted annual salary (in thousands of dollars). What is the predicted salary for someone with 8 years of experience?

Solution:

y^=3.2(8)+1.5=25.6+1.5=27.1\hat{y} = 3.2(8) + 1.5 = 25.6 + 1.5 = 27.1

Since y^\hat{y} is in thousands of dollars, the predicted salary is \27,100$.

Key concept: Using a regression equation to make predictions. The slope (3.2) means salary increases by approximately $3,200 per additional year of experience.

Common mistakes:

  • Forgetting that y^\hat{y} is in thousands (answering $27.1 or $271 instead of $27,100)
  • Incorrect computation: 3.2×8=25.63.2 \times 8 = 25.6, not 24.624.6
  • Confusing the slope and y-intercept

Problem 17: Probability

A bag contains 4 red marbles, 6 blue marbles, and 5 green marbles. Two marbles are drawn at random without replacement. What is the probability that both marbles are blue?

Solution:

Total marbles: 4+6+5=154 + 6 + 5 = 15.

Probability the first is blue: 615=25\frac{6}{15} = \frac{2}{5}.

After removing one blue marble, 14 marbles remain, 5 of which are blue.

Probability the second is blue: 514\frac{5}{14}.

P(both blue)=615×514=25×514=1070=17P(\text{both blue}) = \frac{6}{15} \times \frac{5}{14} = \frac{2}{5} \times \frac{5}{14} = \frac{10}{70} = \frac{1}{7}

Key concept: Probability of dependent events (without replacement). Multiply the conditional probabilities.

Common mistakes:

  • Using replacement: 615×615=36225\frac{6}{15} \times \frac{6}{15} = \frac{36}{225} (incorrect)
  • Not reducing 615\frac{6}{15} before multiplying, leading to 30210=17\frac{30}{210} = \frac{1}{7} (same answer but more error-prone)
  • Forgetting that “without replacement” changes the denominator and numerator for the second draw

Problem 18: Statistics

The five numbers 3,7,a,11,153, 7, a, 11, 15 have a mean of 10. What is the value of aa?

Solution:

Mean=3+7+a+11+155=10\text{Mean} = \frac{3 + 7 + a + 11 + 15}{5} = 10

36+a5=10\frac{36 + a}{5} = 10

36+a=5036 + a = 50

a=14a = 14

Key concept: The mean is the sum of values divided by the count. Use the given mean to find the missing value.

Common mistakes:

  • Addition errors in 3+7+11+153 + 7 + 11 + 15 (it equals 36)
  • Multiplying 10×5=5010 \times 5 = 50 incorrectly
  • Placing aa in the wrong position when computing the median instead (the question asks for the mean)

Problem 19: Statistics — IQR

A dataset has the following five-number summary: minimum = 12, Q1=18Q_1 = 18, median = 24, Q3=32Q_3 = 32, maximum = 45. What is the interquartile range (IQR)?

Solution:

IQR=Q3Q1=3218=14\text{IQR} = Q_3 - Q_1 = 32 - 18 = 14

Key concept: The interquartile range measures the spread of the middle 50% of data.

Common mistakes:

  • Using maximum minus minimum (4512=3345 - 12 = 33), which is the range, not the IQR
  • Using median minus Q1Q_1 (2418=624 - 18 = 6), which is only half the IQR
  • Confusing Q1Q_1 and Q3Q_3 and computing 1832=1418 - 32 = -14 (IQR is always non-negative)

Problem 20: Two-Way Tables

A survey of 200 students found the following distribution:

Prefers SciencePrefers LiteratureTotal
Year 104060100
Year 115050100
Total90110200

What fraction of the Year 10 students prefer Science?

Solution:

Year 10 total = 100. Year 10 students who prefer Science = 40.

40100=25\frac{40}{100} = \frac{2}{5}

Key concept: Reading a two-way table and computing a conditional probability/fraction from a specific row.

Common mistakes:

  • Using the total Science count: 40/9040/90 (this is the fraction of Science-preferring students who are in Year 10, not the question asked)
  • Using the total of all students: 40/200=1/540/200 = 1/5
  • Confusing rows and columns

Geometry and Trigonometry

Problem 21: Area of Composite Shapes

A rectangle has length 12 and width 8. A semicircle is constructed on one of the longer sides as its diameter. What is the total area of the composite shape? (Use π3.14\pi \approx 3.14.)

Solution:

Area of rectangle: 12×8=9612 \times 8 = 96.

The semicircle has diameter 12, so radius r=6r = 6.

Area of semicircle: 12πr2=12(3.14)(36)=56.52\frac{1}{2}\pi r^2 = \frac{1}{2}(3.14)(36) = 56.52.

Total area: 96+56.52=152.5296 + 56.52 = 152.52.

Key concept: Decomposing a composite shape into familiar figures and summing their areas.

Common mistakes:

  • Using diameter instead of radius (r=6r = 6, not 1212)
  • Forgetting the 12\frac{1}{2} factor for a semicircle
  • Using the shorter side (8) as the diameter instead of the longer side (12)

Problem 22: Circle Theorems

A circle has centre OO. Points AA, BB, and CC lie on the circle such that angle AOC=140°AOC = 140°. What is the measure of angle ABCABC?

Solution:

Angle AOC=140°AOC = 140° is a central angle. The arc ACAC has measure 140°140°.

Angle ABCABC is an inscribed angle that subtends the same arc ACAC.

An inscribed angle is half the measure of its intercepted arc:

ABC=140°2=70°\angle ABC = \frac{140°}{2} = 70°

Key concept: The Inscribed Angle Theorem — an inscribed angle is half the central angle that subtends the same arc.

Common mistakes:

  • Assuming the inscribed angle equals the central angle (answering 140°140°)
  • Dividing by the wrong number or misidentifying which arc is subtended
  • Confusing inscribed and central angles when the vertex is on vs. at the centre

Problem 23: Angle Relationships

Two parallel lines are cut by a transversal. One of the eight angles formed measures 125°125°. What is the measure of an angle adjacent to this one?

Solution:

Adjacent angles formed by intersecting lines are supplementary (they sum to 180°180°).

180°125°=55°180° - 125° = 55°

The adjacent angle measures 55°55°.

Key concept: Linear pairs formed by intersecting lines are supplementary.

Common mistakes:

  • Assuming adjacent angles are equal (confusing with vertical angles, which are equal)
  • Selecting 125°125° without recognising the question asks for the adjacent angle
  • Forgetting that this applies regardless of whether the lines are parallel (adjacent angles are always supplementary)

Problem 24: Right Triangle Trigonometry

In right triangle ABCABC with right angle at CC, the hypotenuse AB=13AB = 13 and leg BC=5BC = 5. What is sin(A)\sin(A)?

Solution:

First find ACAC using the Pythagorean theorem:

AC2+BC2=AB2AC^2 + BC^2 = AB^2

AC2+25=169AC^2 + 25 = 169

AC2=144AC^2 = 144

AC=12AC = 12

For angle AA: opposite side is BC=5BC = 5, hypotenuse is AB=13AB = 13.

sin(A)=oppositehypotenuse=513\sin(A) = \frac{\text{opposite}}{\text{hypotenuse}} = \frac{5}{13}

Key concept: Applying SOH CAH TOA and the Pythagorean theorem in a right triangle.

Common mistakes:

  • Using ACAC (adjacent) instead of BCBC (opposite) for sin(A)\sin(A)
  • Computing cos(A)=12/13\cos(A) = 12/13 instead of sin(A)=5/13\sin(A) = 5/13
  • Confusing which angle is AA (the angle at vertex AA, not at BB)

Problem 25: Similar Triangles

Triangle ABCABC is similar to triangle DEFDEF with a scale factor of 2:32:3 (every length in ABCABC is 23\frac{2}{3} of the corresponding length in DEFDEF). If the area of ABCABC is 24 square units, what is the area of DEFDEF?

Solution:

The ratio of areas of similar figures equals the square of the ratio of corresponding lengths.

Area of ABCArea of DEF=(23)2=49\frac{\text{Area of } ABC}{\text{Area of } DEF} = \left(\frac{2}{3}\right)^2 = \frac{4}{9}

24Area of DEF=49\frac{24}{\text{Area of } DEF} = \frac{4}{9}

Area of DEF=24×94=6×9=54\text{Area of } DEF = 24 \times \frac{9}{4} = 6 \times 9 = 54

The area of DEFDEF is 54 square units.

Key concept: The area ratio of similar figures is the square of the length ratio.

Common mistakes:

  • Using the length ratio directly (24×32=3624 \times \frac{3}{2} = 36) instead of squaring it
  • Squaring the wrong ratio (94\frac{9}{4} vs. 49\frac{4}{9})
  • Setting up the proportion inverted: Area of DEFArea of ABC=49\frac{\text{Area of } DEF}{\text{Area of } ABC} = \frac{4}{9}

Problem 26: Volume and Surface Area

A right circular cylinder has radius 5 cm and height 12 cm. What is the total surface area of the cylinder? (Use π3.14\pi \approx 3.14.)

Solution:

Total surface area = lateral area ++ areas of two bases.

Lateral area: 2πrh=2(3.14)(5)(12)=376.82\pi rh = 2(3.14)(5)(12) = 376.8

Area of each base: πr2=(3.14)(25)=78.5\pi r^2 = (3.14)(25) = 78.5

Total: 376.8+2(78.5)=376.8+157=533.8376.8 + 2(78.5) = 376.8 + 157 = 533.8 cm².

Key concept: Surface area of a cylinder = 2πrh+2πr22\pi rh + 2\pi r^2.

Common mistakes:

  • Forgetting to include both circular bases (omitting the factor of 2 on πr2\pi r^2)
  • Using the diameter (10) instead of the radius (5)
  • Computing volume (πr2h\pi r^2 h) instead of surface area

Problem 27: Similar Triangles and Midsegments

In triangle PQRPQR, point MM is the midpoint of PQPQ and point NN is the midpoint of PRPR. If QR=16QR = 16, what is the length of MNMN?

Solution:

The segment connecting the midpoints of two sides of a triangle (the midsegment) is parallel to the third side and half its length.

MN=12×QR=12×16=8MN = \frac{1}{2} \times QR = \frac{1}{2} \times 16 = 8

Key concept: The Triangle Midsegment Theorem.

Common mistakes:

  • Assuming MN=QR=16MN = QR = 16 (it is half, not equal)
  • Assuming MN=14QR=4MN = \frac{1}{4} QR = 4
  • Confusing which side MNMN is parallel to (MNQRMN \parallel QR since MM and NN are midpoints of the other two sides)

Problem 28: Angle Relationships in Polygons

What is the sum of the interior angles of a regular octagon?

Solution:

Sum of interior angles of an nn-sided polygon:

S=(n2)×180°S = (n - 2) \times 180°

For an octagon (n=8n = 8):

S=(82)×180°=6×180°=1080°S = (8 - 2) \times 180° = 6 \times 180° = 1080°

Each interior angle of a regular octagon: 1080°÷8=135°1080° \div 8 = 135°.

Key concept: The polygon interior angle sum formula.

Common mistakes:

  • Using (n1)×180°=1260°(n - 1) \times 180° = 1260° (incorrect formula)
  • Using n×180°=1440°n \times 180° = 1440° (incorrect formula)
  • Confusing interior and exterior angles (exterior angle sum is always 360°360°)

Problem 29: Right Triangle Trigonometry — Application

A ladder leans against a wall, making a 72°72° angle with the ground. If the foot of the ladder is 4 feet from the base of the wall, how long is the ladder?

Solution:

The ground, wall, and ladder form a right triangle. The ladder is the hypotenuse.

The distance from the wall (4 ft) is the side adjacent to the 72°72° angle.

cos(72°)=adjacenthypotenuse=4L\cos(72°) = \frac{\text{adjacent}}{\text{hypotenuse}} = \frac{4}{L}

L=4cos(72°)L = \frac{4}{\cos(72°)}

cos(72°)0.309\cos(72°) \approx 0.309

L=40.30912.94L = \frac{4}{0.309} \approx 12.94

The ladder is approximately 13 feet long.

Key concept: Choosing the correct trigonometric ratio based on which sides are known. Since we know the adjacent side and want the hypotenuse, we use cosine.

Common mistakes:

  • Using sin(72°)\sin(72°) or tan(72°)\tan(72°) instead of cos(72°)\cos(72°) (identifying the wrong sides)
  • Computing cos(72°)\cos(72°) incorrectly
  • Placing 4 in the numerator without the cosine function: L=4×cos(72°)1.24L = 4 \times \cos(72°) \approx 1.24 (this would be the distance from the wall to the top of the ladder, not the ladder length)

Problem 30: Circle Equation

A circle has the equation x2+y26x+8y11=0x^2 + y^2 - 6x + 8y - 11 = 0. What is the radius of this circle?

Solution:

Complete the square for both xx and yy.

Group xx terms and yy terms, move the constant:

(x26x)+(y2+8y)=11(x^2 - 6x) + (y^2 + 8y) = 11

Complete the square for xx: x26x+9=(x3)2x^2 - 6x + 9 = (x - 3)^2 (add 9 to both sides)

Complete the square for yy: y2+8y+16=(y+4)2y^2 + 8y + 16 = (y + 4)^2 (add 16 to both sides)

(x3)2+(y+4)2=11+9+16=36(x - 3)^2 + (y + 4)^2 = 11 + 9 + 16 = 36

This gives centre (3,4)(3, -4) and radius r=36=6r = \sqrt{36} = 6.

Key concept: Converting the expanded form of a circle equation to standard form by completing the square.

Common mistakes:

  • Sign errors when completing the square: x26xx^2 - 6x requires adding (3)2=9(-3)^2 = 9, giving (x3)2(x - 3)^2
  • Forgetting to add the same constants to the right side of the equation
  • Taking the square root of 36 incorrectly, or confusing radius with diameter

Summary

DomainProblemsKey Topics
Algebra1-6Linear equations, systems, inequalities, absolute value
Advanced Math7-13Quadratics, polynomials, exponentials, function composition, rational equations
Problem Solving and Data Analysis14-20Percentages, unit conversions, regression, probability, statistics, two-way tables
Geometry and Trigonometry21-30Composite areas, circle theorems, similar triangles, trigonometry, volume, polygon angles

The most effective approach to these problems is:

  1. Identify the concept before reaching for a formula.
  2. Write out every step — the SAT rewards accuracy over speed.
  3. Check your answer by substituting back or estimating whether the result is reasonable.
  4. Review the common mistakes for each problem type — most errors fall into predictable patterns.

Worked Examples

Worked examples demonstrating the application of key concepts are covered in the detailed sub-pages linked above.

Common Pitfalls

  • Confusing terminology or concepts that appear similar but have distinct meanings.
  • Overlooking key assumptions or boundary conditions that limit applicability.