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Difference between revisions of "2021 Fall AMC 10A Problems"

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==Problem 5==
 
==Problem 5==
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The six-digit number <math>\underline{2}\,\underline{0}\,\underline{2}\,\underline{1}\,\underline{0}\,\underline{A}</math> is prime for only one digit <math>A.</math> What is <math>A?</math>
  
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<math>\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }</math>
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<math>(\textbf{A})\: 1\qquad(\textbf{B}) \: 3\qquad(\textbf{C}) \: 5 \qquad(\textbf{D}) \: 7\qquad(\textbf{E}) \: 9</math>
  
 
[[2021 Fall AMC 10A Problems/Problem 5|Solution]]
 
[[2021 Fall AMC 10A Problems/Problem 5|Solution]]

Revision as of 17:53, 22 November 2021

2021 Fall AMC 10A (Answer Key)
Printable versions: Wiki • Fall AoPS Resources • Fall PDF

Instructions

  1. This is a 25-question, multiple choice test. Each question is followed by answers marked A, B, C, D and E. Only one of these is correct.
  2. You will receive 6 points for each correct answer, 2.5 points for each problem left unanswered if the year is before 2006, 1.5 points for each problem left unanswered if the year is after 2006, and 0 points for each incorrect answer.
  3. No aids are permitted other than scratch paper, graph paper, ruler, compass, protractor and erasers (and calculators that are accepted for use on the SAT if before 2006. No problems on the test will require the use of a calculator).
  4. Figures are not necessarily drawn to scale.
  5. You will have 75 minutes working time to complete the test.
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25

Problem 1

What is the value of $\frac{(2112-2021)^2}{169}$?

$\textbf{(A) } 7 \qquad\textbf{(B) } 21 \qquad\textbf{(C) } 49 \qquad\textbf{(D) } 64 \qquad\textbf{(E) } 91$

Solution

Problem 2

Menkara has a $4 \times 6$ index card. If she shortens the length of one side of this card by $1$ inch, the card would have area $18$ square inches. What would the area of the card be in square inches if instead she shortens the length of the other side by $1$ inch?

$\textbf{(A) }16\qquad\textbf{(B) }17\qquad\textbf{(C) }18\qquad\textbf{(D) }19\qquad\textbf{(E) }20$

Solution

Problem 3

What is the maximum number of balls of clay of radius $2$ that can completely fit inside a cube of side length $6$ assuming the balls can be reshaped but not compressed before they are packed in the cube?

$\textbf{(A) }3\qquad\textbf{(B) }4\qquad\textbf{(C) }5\qquad\textbf{(D) }6\qquad\textbf{(E) }7$

Solution

Problem 4

Mr. Lopez has a choice of two routes to get to work. Route A is $6$ miles long, and his average speed along this route is $30$ miles per hour. Route B is $5$ miles long, and his average speed along this route is $40$ miles per hour, except for a $\frac{1}{2}$-mile stretch in a school zone where his average speed is $20$ miles per hour. By how many minutes is Route B quicker than Route A?

$\textbf{(A)}\ 2 \frac{3}{4} \qquad\textbf{(B)}\ 3 \frac{3}{4} \qquad\textbf{(C)}\ 4 \frac{1}{2} \qquad\textbf{(D)}\ 5 \frac{1}{2} \qquad\textbf{(E)}\ 6 \frac{3}{4}$

Solution

Problem 5

The six-digit number $\underline{2}\,\underline{0}\,\underline{2}\,\underline{1}\,\underline{0}\,\underline{A}$ is prime for only one digit $A.$ What is $A?$

$(\textbf{A})\: 1\qquad(\textbf{B}) \: 3\qquad(\textbf{C}) \: 5 \qquad(\textbf{D}) \: 7\qquad(\textbf{E}) \: 9$

Solution

Problem 6

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 7

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 8

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 9

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 10

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 11

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 12

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 13

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 14

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 15

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 16

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 17

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 18

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 19

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 20

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 21

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 22

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 23

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 24

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

Problem 25

$\textbf{(A) } \qquad\textbf{(B) } \qquad\textbf{(C) } \qquad\textbf{(D) } \qquad\textbf{(E) }$

Solution

See also

2021 AMC 10A (Problems • Answer Key • Resources)
Preceded by
2020 AMC 10B 		Followed by
2021 AMC 10B
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25
All AMC 10 Problems and Solutions

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