2020 AMC 10A Exam Problems

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Used with permission of the Mathematical Association of America.

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1:15:00

1.

What value of xx satisfies x34=51213?x- \frac{3}{4} = \frac{5}{12} - \frac{1}{3}?

23\displaystyle -\frac{2}{3}

736\displaystyle \frac{7}{36}

712\displaystyle \frac{7}{12}

23\displaystyle \frac{2}{3}

56\displaystyle \frac{5}{6}

Answer: E
Solution(s):

Solution 1. Hello

It's nice.

Solution 2. Hi again

I'm back.

2.

The numbers 3,5,7,a,3, 5, 7, a, and bb have an average (arithmetic mean) of 15.15. What is the average of aa and b?b?

00

1515

3030

4545

6060

Answer: C
Solution(s):

Just do it.

3.

Assuming a3,a\neq3, b4,b\neq4, and c5,c\neq5, what is the value in simplest form of the following expression? a35cb43ac54b\frac{a-3}{5-c} \cdot \frac{b-4}{3-a} \cdot \frac{c-5}{4-b}

1-1

11

abc60\displaystyle \frac{abc}{60}

1abc160\displaystyle \frac{1}{abc} - \frac{1}{60}

1601abc\displaystyle \frac{1}{60} - \frac{1}{abc}

Answer: A
Solution(s):

Just do it.

4.

A driver travels for 22 hours at 6060 miles per hour, during which her car gets 3030 miles per gallon of gasoline. She is paid $0.50\$0.50 per mile, and her only expense is gasoline at $2.00\$2.00 per gallon. What is her net rate of pay, in dollars per hour, after this expense?

2020

2222

2424

2525

2626

Answer: E
Solution(s):

Just do it.

5.

What is the sum of all real numbers xx for which x212x+34=2?|x^2-12x+34|=2?

1212

1515

1818

2121

2525

Answer: C
Solution(s):

Just do it.

6.

How many 44-digit positive integers (that is, integers between 10001000 and 9999,9999, inclusive) having only even digits are divisible by 5?5?

8080

100100

125125

200200

500500

Answer: B
Solution(s):

Just do it.

7.

The 2525 integers from 10-10 to 14,14, inclusive, can be arranged to form a 55-by-55 square in which the sum of the numbers in each row, the sum of the numbers in each column, and the sum of the numbers along each of the main diagonals are all the same. What is the value of this common sum?

22

55

1010

2525

5050

Answer: C
Solution(s):

Just do it.

8.

What is the value of 1+2+34+5+6+78++197+198+199200?\begin{align*} &1+2+3-4 +5+6+7-8\\ &+\cdots+197+198+199-200? \end{align*}

9,8009,800

9,9009,900

10,00010,000

10,10010,100

10,20010,200

Answer: B
Solution(s):

Just do it.

9.

A single bench section at a school event can hold either 77 adults or 1111 children. When NN bench sections are connected end to end, an equal number of adults and children seated together will occupy all the bench space. What is the least possible positive integer value of N?N?

99

1818

2727

3636

7777

Answer: B
Solution(s):

Just do it.

10.

Seven cubes, whose volumes are 1,1, 8,8, 27,27, 64,64, 125,125, 216,216, and 343343 cubic units, are stacked vertically to form a tower in which the volumes of the cubes decrease from bottom to top. Except for the bottom cube, the bottom face of each cube lies completely on top of the cube below it. What is the total surface area of the tower (including the bottom) in square units?

644644

658658

664664

720720

749749

Answer: B
Solution(s):

Just do it.

11.

What is the median of the following list of 40404040 numbers?? 1,2,3,,2020,12,22,32,,20202\begin{align*} &1, 2, 3, \ldots, 2020, \\&1^2, 2^2, 3^2, \ldots, 2020^2 \end{align*}

1974.51974.5

1975.51975.5

1976.51976.5

1977.51977.5

1978.51978.5

Answer: C
Solution(s):

Just do it.

12.

Triangle AMCAMC is isosceles with AM=AC.AM = AC. Medians MV\overline{MV} and CU\overline{CU} are perpendicular to each other, and MV=CU=12.MV=CU=12. What is the area of AMC?\triangle AMC?

4848

7272

9696

144144

192192

Answer: C
Solution(s):

Just do it.

13.

A frog sitting at the point (1,2)(1, 2) begins a sequence of jumps, where each jump is parallel to one of the coordinate axes and has length 1,1, and the direction of each jump (up, down, right, or left) is chosen independently at random. The sequence ends when the frog reaches a side of the square with vertices (0,0),(0, 0), (0,4),(0, 4), (4,4),(4, 4), and (4,0).(4, 0). What is the probability that the sequence of jumps ends on a vertical side of the square?

12\displaystyle \frac{1}{2}

58\displaystyle \frac{5}{8}

23\displaystyle \frac{2}{3}

34\displaystyle \frac{3}{4}

78\displaystyle \frac{7}{8}

Answer: B
Solution(s):

Just do it.

14.

Real numbers xx and yy satisfy x+y=4x + y = 4 and xy=2.x \cdot y = -2. What is the value of

x+x3y2+y3x2+y?x + \frac{x^3}{y^2} + \frac{y^3}{x^2} + y?

360360

400400

420420

440440

480480

Answer: D
Solution(s):

Just do it.

15.

A positive integer divisor of 12!12! is chosen at random. The probability that the divisor chosen is a perfect square can be expressed as mn,\frac{m}{n}, where mm and nn are relatively prime positive integers. What is m+n?m+n?

33

55

1212

1818

2323

Answer: E
Solution(s):

Just do it.

16.

A point is chosen at random within the square in the coordinate plane whose vertices are (0,0),(0, 0), (2020,0),(2020, 0), (2020,2020),(2020, 2020), and (0,2020).(0, 2020). The probability that the point is within dd units of a lattice point is 12.\tfrac{1}{2}. (A point (x,y)(x, y) is a lattice point if xx and yy are both integers.) What is dd to the nearest tenth??

0.30.3

0.40.4

0.50.5

0.60.6

0.70.7

Answer: B
Solution(s):

Just do it.

17.

Define P(x)=(x12)(x22)(x1002)\begin{align*} P(x) =&(x-1^2)(x-2^2)\\&\cdots(x-100^2) \end{align*} How many integers nn are there such that P(n)0?P(n)\leq 0?

49004900

49504950

50005000

50505050

51005100

Answer: E
Solution(s):

Just do it.

18.

Let (a,b,c,d)(a,b,c,d) be an ordered quadruple of not necessarily distinct integers, each one of them in the set {0,1,2,3}.\{0,1,2,3\}. For how many such quadruples is it true that adbca\cdot d-b\cdot c is odd? (For example, (0,3,1,1)(0,3,1,1) is one such quadruple, because 0131=30\cdot 1-3\cdot 1 = -3 is odd.)

4848

6464

9696

128128

192192

Answer: C
Solution(s):

Just do it.

19.

As shown in the figure below, a regular dodecahedron (the polyhedron consisting of 1212 congruent regular pentagonal faces) floats in space with two horizontal faces. Note that there is a ring of five slanted faces adjacent to the top face, and a ring of five slanted faces adjacent to the bottom face. How many ways are there to move from the top face to the bottom face via a sequence of adjacent faces so that each face is visited at most once and moves are not permitted from the bottom ring to the top ring?

125125

250250

405405

640640

810810

Answer: E
Solution(s):

Just do it.

20.

Quadrilateral ABCDABCD satisfies ABC=ACD=90,AC=20,\angle ABC = \angle ACD = 90^{\circ}, AC=20, and CD=30.CD=30. Diagonals AC\overline{AC} and BD\overline{BD} intersect at point E,E, and AE=5.AE=5. What is the area of quadrilateral ABCD?ABCD?

330330

340340

350350

360360

370370

Answer: D
Solution(s):

Just do it.

21.

There exists a unique strictly increasing sequence of nonnegative integers a1<a2<<aka_1 < a_2 < … < a_k such that2289+1217+1=2a1+2a2++2ak.\frac{2^{289}+1}{2^{17}+1} = 2^{a_1} + 2^{a_2} + … + 2^{a_k}.What is k?k?

117117

136136

137137

273273

306306

Answer: C
Solution(s):

Just do it.

22.

For how many positive integers n1000n \le 1000 is998n+999n+1000n\left\lfloor \dfrac{998}{n} \right\rfloor+\left\lfloor \dfrac{999}{n} \right\rfloor+\left\lfloor \dfrac{1000}{n}\right \rfloornot divisible by 3?3? (Recall that x\lfloor x \rfloor is the greatest integer less than or equal to x.x.)

2222

2323

2424

2525

2626

Answer: A
Solution(s):

Just do it.

23.

Let TT be the triangle in the coordinate plane with vertices (0,0),(4,0),(0,0), (4,0), and (0,3).(0,3). Consider the following five isometries (rigid transformations) of the plane: rotations of 90,180,90^{\circ}, 180^{\circ}, and 270270^{\circ} counterclockwise around the origin, reflection across the xx-axis, and reflection across the yy-axis. How many of the 125125 sequences of three of these transformations (not necessarily distinct) will return TT to its original position? (For example, a 180180^{\circ} rotation, followed by a reflection across the xx-axis, followed by a reflection across the yy-axis will return TT to its original position, but a 9090^{\circ} rotation, followed by a reflection across the xx-axis, followed by another reflection across the xx-axis will not return TT to its original position.)

1212

1515

1717

2020

2525

Answer: A
Solution(s):

Just do it.

24.

Let nn be the least positive integer greater than 10001000 for which

gcd(63,n+120)=21\gcd(63, n+120) =21

and

gcd(n+63,120)=60.\gcd(n+63, 120)=60.

What is the sum of the digits of n?n?

1212

1515

1818

2121

2424

Answer: C
Solution(s):

Just do it.

25.

Jason rolls three fair standard six-sided dice. Then he looks at the rolls and chooses a subset of the dice (possibly empty, possibly all three dice) to reroll. After rerolling, he wins if and only if the sum of the numbers face up on the three dice is exactly 7.7. Jason always plays to optimize his chances of winning. What is the probability that he chooses to reroll exactly two of the dice?

736\displaystyle \frac{7}{36}

524\displaystyle \frac{5}{24}

29\displaystyle \frac{2}{9}

1722\displaystyle \frac{17}{22}

14\displaystyle \frac{1}{4}

Answer: A
Solution(s):

Just do it.