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AMC 10B 2020
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Number Theory
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Geometry
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1
Algebra
오답
What is the value of \( 1 - ( - 2 ) - 3 - ( - 4 ) - 5 - ( - 6 ) ? \)
A
\(- 20\)
B
\(- 3\)
C
\(3\)
\(5\)
정답
E
\(21\)
해설 없음
2
Geometry
오답
Carl has \(5\) cubes each having side length \(1\), and Kate has \(5\) cubes
each having side length \(2\). What is the total volume of these \(10\)
cubes?
A
\(24\)
B
\(25\)
C
\(28\)
D
\(40\)
\(45\)
정답
해설 없음
3
Algebra
오답
The ratio of \(w\) to \(x\) is \(4 : 3\), the ratio of \(y\) to \(z\) is \(3 : 2\),
and the ratio of \(z\) to \(x\) is \(1 : 6\). What is the ratio of \(w\) to
\(y ?\)
A
\(4 : 3\)
B
\(3 : 2\)
C
\(8 : 3\)
D
\(4 : 1\)
\(16 : 3\)
정답
해설 없음
4
Number Theory
오답
The acute angles of a right triangle are \(a^\circ\) and \(b^\circ\),
where \(a > b\) and both \(a\) and \(b\) are prime numbers. What is the least
possible value of \(b\)?
A
\(2\)
B
\(3\)
C
\(5\)
\(7\)
정답
E
\(11\)
해설 없음
5
Counting and Probability
오답
How many distinguishable arrangements are there of \(1\) brown tile, \(1\)
purple tile, \(2\) green tiles, and \(3\) yellow tiles in a row from left to
right? (Tiles of the same color are indistinguishable.)
A
\(210\)
\(420\)
정답
C
\(630\)
D
\(840\)
E
\(1050\)
해설 없음
6
Number Theory
오답
Driving along a highway, Megan noticed that her odometer showed \(15951\)
(miles). This number is a palindrome-it reads the same forward and
backward. Then \(2\) hours later, the odometer displayed the next higher
palindrome. What was her average speed, in miles per hour, during this
\(2\)-hour period?
A
\(50\)
\(55\)
정답
C
\(60\)
D
\(65\)
E
\(70\)
해설 없음
7
Number Theory
오답
How many positive even multiples of \(3\) less than \(2020\) are perfect
squares?
\(7\)
정답
B
\(8\)
C
\(9\)
D
\(10\)
E
\(12\)
해설 없음
8
Geometry
오답
Points \(P\) and \(Q\) lie in a plane with \(P Q = 8\). How many locations for
point \(R\) in this plane are there such that the triangle with vertices
\(P\), \(Q\), and \(R\) is a right triangle with area \(12\) square units?
A
\(2\)
B
\(4\)
C
\(6\)
\(8\)
정답
E
\(12\)
해설 없음
9
Number Theory
오답
How many ordered pairs of integers \(( x , y )\) satisfy the equation
\( x^2020 + y^2 = 2 y ? \)
A
\(1\)
B
\(2\)
C
\(3\)
\(4\)
정답
E
\(\text{infinitely many}\)
해설 없음
10
Geometry
오답
A three-quarter sector of a circle of radius \(4\) inches together with
its interior can be rolled up to form the lateral surface area of a
right circular cone by taping together along the two radii shown. What
is the volume of the cone in cubic inches?
A
\(3 \pi \sqrt{5}\)
B
\(4 \pi \sqrt{3}\)
\(3 \pi \sqrt{7}\)
정답
D
\(6 \pi \sqrt{3}\)
E
\(6 \pi \sqrt{7}\)
해설 없음
11
Counting and Probability
오답
Ms.~Carr asks her students to read any \(5\) of the \(10\) books on a
reading list. Harold randomly selects \(5\) books from this list, and
Betty does the same. What is the probability that there are exactly \(2\)
books that they both select?
A
\(\dfrac{1}{8}\)
B
\(\dfrac{5}{36}\)
C
\(\dfrac{14}{45}\)
\(\dfrac{25}{63}\)
정답
E
\(\dfrac{1}{2}\)
해설 없음
12
Number Theory
오답
The decimal representation of \( \dfrac{1}{2}0^20 \) consists of a string of
zeros after the decimal point, followed by a \(9\) and then several more
digits. How many zeros are in that initial string of zeros after the
decimal point?
A
\(23\)
B
\(24\)
C
\(25\)
\(26\)
정답
E
\(27\)
해설 없음
13
Geometry
오답
Andy the Ant lives on a coordinate plane and is currently at
\(( - 20 , 20 )\) facing east (that is, in the positive \(x\)-direction).
Andy moves \(1\) unit and then turns \(90^\circ\) left. From there, Andy
moves \(2\) units (north) and then turns \(90^\circ\) left. He then moves
\(3\) units (west) and again turns \(90^\circ\) left. Andy continues his
progress, increasing his distance each time by \(1\) unit and always
turning left. What is the location of the point which Andy makes the
\(2020\) left turn? \(\mathbf{\text{(E)}} ( - 1022 , - 994 )\)
A
\(( - 1030 , - 994 )\)
\(( - 1030 , - 990 )\)
정답
C
\(( - 1026 , - 994 )\)
D
\(( - 1026 , - 990 )\)
해설 없음
14
Geometry
오답
As shown in the figure below, six semicircles lie in the interior of a
regular hexagon with side length 2 so that the diameters of the
semicircles coincide with the sides of the hexagon. What is the area of
the shaded region --- inside the hexagon but outside all of the
semicircles?
A
\(6 \sqrt{3} - 3 \pi\)
B
\(\dfrac{9 \sqrt{3}}{2} - 2 \pi\)
C
\(\dfrac{3 \sqrt{3}}{2} - \dfrac{\pi}{3}\)
\(3 \sqrt{3} - \pi\)
정답
E
\(\dfrac{9 \sqrt{3}}{2} - \pi\)
해설 없음
15
Number Theory
오답
Steve wrote the digits \(1\), \(2\), \(3\), \(4\), and \(5\) in order repeatedly
from left to right, forming a list of \(10 , 000\) digits, beginning
\(123451234512 \cdots .\) He then erased every third digit from his list
(that is, the \(3\)rd, \(6\)th, \(9\)th, \(\cdots\) digits from the left), then
erased every fourth digit from the resulting list (that is, the \(4\)th,
\(8\)th, \(12\)th, \(\cdots\) digits from the left in what remained), and then
erased every fifth digit from what remained at that point. What is the
sum of the three digits that were then in the positions
\(2019 , 2020 , 2021\)?
A
\(7\)
B
\(9\)
C
\(10\)
\(11\)
정답
E
\(12\)
해설 없음
16
Counting and Probability
오답
Bela and Jenn play the following game on the closed interval
\([ 0 , n ]\) of the real number line, where \(n\) is a fixed integer
greater than \(4\). They take turns playing, with Bela going first. At his
first turn, Bela chooses any real number in the interval \([ 0 , n ]\).
Thereafter, the player whose turn it is chooses a real number that is
more than one unit away from all numbers previously chosen by either
player. A player unable to choose such a number loses. Using optimal
strategy, which player will win the game?
\(\mathbf{\text{(D)}} \text{ Jenn will win if and only if } n \text{ is odd.} #h(2em) \mathbf{\text{(E)}} \text{ Jenn will win if and only if } n > 8 .\)
\(\text{ Bela will always win.}\)
정답
B
\(\text{ Jenn will always win.}\)
C
\(\text{ Bela will win if and only if } n \text{ is odd.}\)
해설 없음
17
Counting and Probability
오답
There are \(10\) people standing equally spaced around a circle. Each
person knows exactly \(3\) of the other \(9\) people: the \(2\) people
standing next to him or her, as well as the person directly across the
circle. How many ways are there for the \(10\) people to split up into \(5\)
pairs so that the members of each pair know each other?
A
\(11\)
B
\(12\)
\(13\)
정답
D
\(14\)
E
\(15\)
해설 없음
18
Counting and Probability
오답
An urn contains one red ball and one blue ball. A box of extra red and
blue balls lies nearby. George performs the following operation four
times: he draws a ball from the urn at random and then takes a ball of
the same color from the box and returns those two matching balls to the
urn. After the four iterations the urn contains six balls. What is the
probability that the urn contains three balls of each color?
A
\(\dfrac{1}{6}\)
\(\dfrac{1}{5}\)
정답
C
\(\dfrac{1}{4}\)
D
\(\dfrac{1}{3}\)
E
\(\dfrac{1}{2}\)
해설 없음
19
Counting and Probability
오답
In a certain card game, a player is dealt a hand of \(10\) cards from a
deck of \(52\) distinct cards. The number of distinct (unordered) hands
that can be dealt to the player can be written as \(158 A 00 A 4 A A 0\).
What is the digit \(A\)?
\(2\)
정답
B
\(3\)
C
\(4\)
D
\(6\)
E
\(7\)
해설 없음
20
Geometry
오답
Let \(B\) be a right rectangular prism (box) with edges lengths \$1,\$3,
and \(4\), together with its interior. For real \(r \geq 0\), let
\(S ( r )\) be the set of points in \(3\)-dimensional space that lie
within a distance \(r\) of some point in \(B\). The volume of \(S ( r )\)
can be expressed as \(a r^3 + b r^2 + c r + d\), where \(a , \) b , \( c ,\) and
\(d\) are positive real numbers. What is \(\dfrac{b c}{a d} ?\)
A
\(6\)
\(19\)
정답
C
\(24\)
D
\(26\)
E
\(38\)
해설 없음
21
Geometry
오답
In square \(A B C D\), points \(E\) and \(H\) lie on \(\overline{A B}\) and
\(\overline{D A}\), respectively, so that \(A E = A H .\) Points \(F\) and \(G\)
lie on \(\overline{B C}\) and \(\overline{C D}\), respectively, and points \(I\)
and \(J\) lie on \(\overline{E H}\) so that
\(\overline{F I} \perp \overline{E H}\) and
\(\overline{G J} \perp \overline{E H}\). See the figure below. Triangle
\(A E H\), quadrilateral \(B F I E\), quadrilateral \(D H J G\), and pentagon
\(F C G J I\) each has area \(1 .\) What is \(F I^2\)?
A
\(\dfrac{7}{3}\)
\(8 - 4 \sqrt{2}\)
정답
C
\(1 + \sqrt{2}\)
D
\(\dfrac{7}{4} \sqrt{2}\)
E
\(2 \sqrt{2}\)
해설 없음
22
Number Theory
오답
What is the remainder when \(2^202 + 202\) is divided by
\(2^101 + 2^51 + 1\)?
A
\(100\)
B
\(101\)
C
\(200\)
\(201\)
정답
E
\(202\)
해설 없음
23
Counting and Probability
오답
Square \(A B C D\) in the coordinate plane has vertices at the points
\(A ( 1 , 1 ) , B ( - 1 , 1 ) , C ( - 1 , - 1 ) ,\) and
\(D ( 1 , - 1 ) .\) Consider the following four transformations:
\(\quad bullet #h(2em) \) L ,\( a rotation of \)90^compose\( counterclockwise around the origin; \)quad bullet #h(2em) \( R ,\) a rotation of \(90^\circ\)
clockwise around the origin; \(\quad bullet #h(2em) \) H ,\( a reflection across the \)x\(-axis; and \)quad bullet #h(2em) \( V ,\) a reflection across
the \(y\)-axis. Each of these transformations maps the squares onto
itself, but the positions of the labeled vertices will change. For
example, applying \(R\) and then \(V\) would send the vertex \(A\) at
\(( 1 , 1 )\) to \(( - 1 , - 1 )\) and would send the vertex \(B\) at
\(( - 1 , 1 )\) to itself. How many sequences of \(20\) transformations
chosen from \(\{ L , R , H , V \}\) will send all of the labeled vertices
back to their original positions? (For example, \(R , R , V , H\) is one
sequence of \(4\) transformations that will send the vertices back to
their original positions.)
A
\(2^37\)
B
\(3 \cdot 2^36\)
\(2^38\)
정답
D
\(3 \cdot 2^37\)
E
\(2^39\)
해설 없음
24
Number Theory
오답
How many positive integers \(n\) satisfy
\( \dfrac{n + 1000}{70} = ⌊ \sqrt{n} ⌋ ? \) (Recall that
\(⌊ x ⌋\) is the greatest integer not exceeding \(x\).)
A
\(2\)
B
\(4\)
\(6\)
정답
D
\(30\)
E
\(32\)
해설 없음
25
Number Theory
오답
Let \(D ( n )\) denote the number of ways of writing the positive
integer \(n\) as a product \( n = f_1 \cdot f_2 \cdots.c f_k , \) where
\(k \geq 1\), the \(f_i\) are integers strictly greater than \(1\), and the
order in which the factors are listed matters (that is, two
representations that differ only in the order of the factors are counted
as distinct). For example, the number \(6\) can be written as \(6\),
\(2 \cdot 3\), and \(3 \cdot 2\), so \(D ( 6 ) = 3\). What is
\(D ( 96 )\)?
\(112\)
정답
B
\(128\)
C
\(144\)
D
\(172\)
E
\(184\)
해설 없음
다시 풀기
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