Difference between revisions of "2017 AMC 10B Problems/Problem 2"

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==Problem==
 
==Problem==
  
Sofia ran <math>5</math> laps around the <math>400</math>-meter track at her school. For each lap, she ran the first <math>100</math> meters at an average speed of <math>4</math> meters per second and the remaining <math>300</math> meters at an average speed of <math>5</math> meters per second. How much time did Sofia take running the <math>5</math> laps?
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Sofia ran <math>5</math> laps around the <math>400</math>-meter track at her school. For each lap, she ran the first <math>100</math> meters at an average speed of <math>4</math> meters per second and the remaining <math>300</math> meters at an average speed of <math>5</math> meters per second. How much time did Sofia take running the <math>5</math> laps?  
  
<math>\textbf{(A)}\ \text{5 minutes and 35 seconds}\qquad\textbf{(B)}\ \text{6 minutes and 40 seconds}\qquad\textbf{(C)}\ \text{7 minutes and 5 seconds}\qquad\textbf{(D)}\ \text{7 minutes and 25 seconds}</math><math>\qquad\textbf{(E)}\ \text{8 minutes and 10 seconds}</math>
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<math>\qquad\textbf{(A)}\ \text{5 minutes and 35 seconds}</math> <br>
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<math>\qquad\textbf{(B)}\ \text{6 minutes and 40 seconds}</math> <br>
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<math>\qquad\textbf{(C)}\ \text{7 minutes and 5 seconds}</math> <br>
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<math>\qquad\textbf{(D)}\ \text{7 minutes and 25 seconds}</math> <br>
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<math>\qquad\textbf{(E)}\ \text{8 minutes and 10 seconds}</math>
  
 
==Solution==
 
==Solution==

Revision as of 22:21, 15 April 2020

Problem

Sofia ran $5$ laps around the $400$-meter track at her school. For each lap, she ran the first $100$ meters at an average speed of $4$ meters per second and the remaining $300$ meters at an average speed of $5$ meters per second. How much time did Sofia take running the $5$ laps?

$\qquad\textbf{(A)}\ \text{5 minutes and 35 seconds}$
$\qquad\textbf{(B)}\ \text{6 minutes and 40 seconds}$
$\qquad\textbf{(C)}\ \text{7 minutes and 5 seconds}$
$\qquad\textbf{(D)}\ \text{7 minutes and 25 seconds}$
$\qquad\textbf{(E)}\ \text{8 minutes and 10 seconds}$

Solution

If Sofia ran the first $100$ meters of each lap at $4$ meters per second and the remaining $300$ meters of each lap at $5$ meters per second, then she took $\frac{100}{4}+\frac{300}{5}=25+60=85$ seconds for each lap. Because she ran $5$ laps, she took a total of $5 \cdot 85=425$ seconds, or $7$ minutes and $5$ seconds. The answer is $\boxed{\textbf{(C)}\ \text{7 minutes and 5 seconds}}$.

See Also

2017 AMC 10B (ProblemsAnswer KeyResources)
Preceded by
Problem 1
Followed by
Problem 3
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All AMC 10 Problems and Solutions

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