Difference between revisions of "2013 AMC 8 Problems/Problem 21"

Revision as of 08:52, 16 July 2024

Problem

Samantha lives 2 blocks west and 1 block south of the southwest corner of City Park. Her school is 2 blocks east and 2 blocks north of the northeast corner of City Park. On school days she bikes on streets to the southwest corner of City Park, then takes a diagonal path through the park to the northeast corner, and then bikes on streets to school. If her route is as short as possible, how many different routes can she take?

$\textbf{(A)}\ 3 \qquad \textbf{(B)}\ 6 \qquad \textbf{(C)}\ 9 \qquad \textbf{(D)}\ 12 \qquad \textbf{(E)}\ 18$

Video Solution by OmegaLearn Using Geometric Counting

https://youtu.be/OOdK-nOzaII?t=2679

~ pi_is_3.14

Video Solution

https://www.youtube.com/watch?v=7hQYzA6lsVc ~David

https://youtu.be/9nveueuZiqs ~savannahsolver

Solution

$[asy] unitsize(8mm); for(int i=0; i<=8; ++i) { draw((0,i)--(8,i)); draw((i,0)--(i,8)); } fill((2,1)--(6,1)--(6,6)--(2,6)--cycle); for(int j=0; j<= 38; ++j) { draw((0,0)--(2,0)--(2,1)--(0,1)--(0,0), black+linewidth(3)); draw((6,6)--(6,8)--(8,8)--(8,6)--(6,6), black+linewidth(3)); }[/asy]$

Using combinations, we get that the number of ways to get from Samantha's house to City Park is $\binom31 = \dfrac{3!}{1!2!} = 3$ , and the number of ways to get from City Park to school is $\binom42= \dfrac{4!}{2!2!} = \dfrac{4\cdot 3}{2} = 6$ . Since there's one way to go through City Park (just walking straight through), the number of different ways to go from Samantha's house to City Park to school $3\cdot 6 = \boxed{\textbf{(E)}\ 18}$ .

2013 AMC 8 (Problems • Answer Key • Resources)
Preceded by Problem 20	Followed by Problem 22
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 AJHSME/AMC 8 Problems and Solutions

The problems on this page are copyrighted by the Mathematical Association of America's American Mathematics Competitions.

@@ Line 14: / Line 14: @@
 https://youtu.be/9nveueuZiqs ~savannahsolver
-==Video Solution for Problems 21-25 By Rohan Dhillon==
-https://youtu.be/-mi3qziCuec
 ==Solution==

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