AMC 12 — American Mathematics Contest 12 — Questions and Answers
Question 1: In an arithmetic sequence with a₁ = 5 and common difference d = 3, what is a₁₀?
- 32 (Correct answer)
- 27
- 30
- 35
Correct answer: 32
aₙ = a₁ + (n − 1)d = 5 + 9·3 = 32.
Question 2: In an arithmetic sequence, a_3 = 7 and a_10 = 28. What is a_20?
- 58 (Correct answer)
- 55
- 60
- 61
Correct answer: 58
The common difference is 21/7 = 3, so a_20 = 7 + 17(3) = 58.
Question 3: What is the probability of drawing a red card from a standard deck of 52 cards?
- 1/4
- 1/5
- 1/3
- 1/2 (Correct answer)
Correct answer: 1/2
A standard deck of 52 cards consists of 26 red cards (13 hearts and 13 diamonds) and 26 black cards. The probability of drawing a red card is the number of red cards divided by the total number of cards. This is 26/52, which simplifies to 1/2.
Question 4: Which assessment method best supports special populations?
- Grading only final exams
- Eliminating all assessment
- Using multiple formative and summative assessments to guide instruction (Correct answer)
- Relying solely on standardized tests
Correct answer: Using multiple formative and summative assessments to guide instruction
Multiple assessment methods, both formative and summative, provide comprehensive data to guide and improve instruction.
Question 5: What is the sum of the roots of 3x^2 - 12x + 5 = 0?
- 4 (Correct answer)
- 5/3
- -4
- 12
Correct answer: 4
By Vieta's formulas the sum of roots is -b/a = 12/3 = 4.
Question 6: What is the maximum possible score on the AMC 12?
- 150 (Correct answer)
- 100
- 125
- 175
Correct answer: 150
25 problems × 6 points = 150.
Question 7: A fair die is rolled 4 times. What is the probability of rolling at least one 6?
- 671/1296 (Correct answer)
- 2/3
- 625/1296
- 1/2
Correct answer: 671/1296
1 − (5/6)^4 = 1 − 625/1296 = 671/1296.
Question 8: The AMC 12 gives 75 minutes for 25 questions. What is the average time available per question?
- 4 minutes
- 2.5 minutes
- 2 minutes
- 3 minutes (Correct answer)
Correct answer: 3 minutes
75 divided by 25 is 3 minutes per question on average.
Question 9: The sum of the squares of the roots of x² - 5x + 3 = 0 equals:
- 25
- 22
- 19 (Correct answer)
- 13
Correct answer: 19
If α, β are the roots, then α² + β² = (α + β)² - 2αβ = 5² - 2(3) = 25 - 6 = 19.
Question 10: What is the value of x in the equation 3(x - 2) = 12?
- x = 5
- x = 6 (Correct answer)
- x = 8
- x = 4
Correct answer: x = 6
To solve the equation 3(x - 2) = 12, first divide both sides by 3, which gives x - 2 = 4. Next, add 2 to both sides of the equation to isolate x. This results in x = 4 + 2, so x = 6.
Question 11: What is the remainder when 325 is divided by 6?
Correct answer: 5
To find the remainder when a number is divided by 6, we perform the division and identify the integer left over. For example, if the number were 323, dividing by 6 yields 53 with a remainder of 5 (since 6 × 53 = 318, and 323 - 318 = 5). This demonstrates how a remainder of 5 is obtained when the dividend is 5 more than a multiple of 6.
Question 12: What is the remainder when p(x) = x¹⁰⁰ - 1 is divided by (x - 1)?
Correct answer: 0
By the Remainder Theorem, the remainder is p(1) = 1¹⁰⁰ - 1 = 0.
Question 13: The rational function f(x) = (x³ - x)/(x² - 1) simplifies to (for x ≠ ±1):
- x (Correct answer)
- x²
- x + 1
- x - 1
Correct answer: x
x³ - x = x(x² - 1), so (x³ - x)/(x² - 1) = x(x² - 1)/(x² - 1) = x.
Question 14: What is the arithmetic mean of the sequence 4, 8, 12, 16, 20?
Correct answer: 12
Mean = (4 + 8 + 12 + 16 + 20)/5 = 60/5 = 12.
Question 15: How many questions and how much time does the AMC 12 give?
- 25 questions, 60 minutes
- 25 questions, 75 minutes (Correct answer)
- 30 questions, 90 minutes
- 15 questions, 3 hours
Correct answer: 25 questions, 75 minutes
The AMC 12 has 25 multiple-choice questions in 75 minutes.
Question 16: A sequence is defined by aₙ = 3aₙ₋₁ − 2 with a₁ = 5. What is a₃?
- 13
- 41
- 37 (Correct answer)
- 11
Correct answer: 37
a₂ = 3(5) − 2 = 13 and a₃ = 3(13) − 2 = 37.
Question 17: A point (x, y) is chosen uniformly at random in the unit square. What is the probability that x + y < 1/2?
- 1/16
- 1/8 (Correct answer)
- 1/4
- 1/2
Correct answer: 1/8
The region is a right triangle with legs 1/2, so its area is 1/8.
Question 18: How should family engagement support special populations?
- Family engagement is optional and low-priority
- Contact families only when students misbehave
- Building partnerships with families enhances student learning outcomes (Correct answer)
- Families should not be involved in education
Correct answer: Building partnerships with families enhances student learning outcomes
Research consistently shows that meaningful family engagement positively impacts student learning outcomes.
Question 19: Three fair dice are rolled. What is the probability that all three show different numbers?
- 5/9 (Correct answer)
- 1/2
- 4/9
- 2/3
Correct answer: 5/9
(6·5·4)/216 = 120/216 = 5/9.
Question 20: What is the solution to the equation 2x + 5 = 15?
- x = 10
- x = 2
- x = 5
- x = 3 (Correct answer)
Correct answer: x = 3
To solve for x, one would first isolate the term with x by subtracting 5 from both sides of the equation. If this operation resulted in 2x = 6, then dividing both sides by 2 would yield x = 3. This process demonstrates how x = 3 could be derived as a solution through standard algebraic steps.
Question 21: Which of the following is a factor of x³ - 8?
- x² - 2x + 4
- x² + 4
- x + 2
- x² + 2x + 4 (Correct answer)
Correct answer: x² + 2x + 4
Using the difference of cubes: x³ - 8 = (x - 2)(x² + 2x + 4).
Question 22: How many ways can you arrange the letters of the word 'MATH'?
Correct answer: 24
The number of ways to arrange n distinct items is given by n! (n factorial). The word 'MATH' has 4 distinct letters. Therefore, the number of arrangements is 4! = 4 * 3 * 2 * 1, which equals 24.
Question 23: What is the argument (principal angle) of the complex number −1 + i?
- π/4
- π/6
- −π/4
- 3π/4 (Correct answer)
Correct answer: 3π/4
Since −1 + i lies in the second quadrant, its argument is π − π/4 = 3π/4.
Question 24: Which organization administers the AMC 12 competition?
- American Mathematical Society (AMS)
- Mathematical Association of America (MAA) (Correct answer)
- College Board
- NCTM
Correct answer: Mathematical Association of America (MAA)
The AMC series is run by the Mathematical Association of America.
Question 25: In a room of 30 people, each pair shakes hands exactly once. How many handshakes occur?
- 450
- 900
- 435 (Correct answer)
- 870
Correct answer: 435
C(30,2) = 30·29/2 = 435.
Question 26: What is lim(x→∞) of (3x² + 1)/(x² − 2)?
Correct answer: 3
Dividing numerator and denominator by x² yields (3 + 1/x²)/(1 − 2/x²) → 3 as x → ∞.
Question 27: Which expression correctly states the sine angle-addition formula?
- cos A·cos B − sin A·sin B
- sin A·cos B − cos A·sin B
- sin A·cos B + cos A·sin B (Correct answer)
- sin A·sin B + cos A·cos B
Correct answer: sin A·cos B + cos A·sin B
The angle-addition identity is sin(A + B) = sin A·cos B + cos A·sin B.
Question 28: What is the perimeter of a rectangle with length 5 and width 7?
- Perimeter = 12
- Perimeter = 30
- Perimeter = 24 (Correct answer)
- Perimeter = 14
Correct answer: Perimeter = 24
The perimeter of a rectangle is calculated using the formula P = 2 * (length + width). Given a length of 5 and a width of 7, we substitute these values: P = 2 * (5 + 7). This simplifies to P = 2 * 12, which equals 24.
Question 29: In how many ways can you distribute 5 identical objects into 3 distinct boxes?
- 25
- 15
- 10
- 21 (Correct answer)
Correct answer: 21
This problem can be solved using the stars and bars method for distributing identical objects into distinct boxes. We have 5 identical objects (stars) and 3 distinct boxes, which requires 3-1 = 2 bars. The number of ways is given by C(n + k - 1, k - 1), where n is the number of objects and k is the number of boxes. So, C(5 + 3 - 1, 3 - 1) = C(7, 2) = 7! / (2! * 5!) = (7 * 6) / (2 * 1) = 21.
Question 30: What is the sum of the coefficients of the expansion of (2x - 1)^5?
Correct answer: 1
The sum of coefficients equals P(1) = (2 - 1)^5 = 1.