Difference between revisions of "2017 AMC 10A Problems/Problem 4"

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<math>\textbf{(A)}\ 13.5\qquad\textbf{(B)}\ 14\qquad\textbf{(C)}\ 14.5\qquad\textbf{(D)}\ 15\qquad\textbf{(E)}\ 15.5</math>
 
<math>\textbf{(A)}\ 13.5\qquad\textbf{(B)}\ 14\qquad\textbf{(C)}\ 14.5\qquad\textbf{(D)}\ 15\qquad\textbf{(E)}\ 15.5</math>
  
==Solution 1==
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==Solution==
  
Every <math>30</math> seconds, <math>3-2=1</math> toys are put in the box, so after <math>27\cdot30</math> seconds, there will be <math>27</math> toys in the box.  Mia's mom will then put <math>3</math> toys into the box, and we have our total amount of time to be <math>27\cdot30+30=840</math> seconds, which equals <math>14</math> minutes. <math>\boxed{(\textbf{B})\ 14}</math>
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Every <math>30</math> seconds, <math>3</math> toys are put in the box and <math>2</math> toys are taken out, so the number of toys increases by <math>3-2=1</math> every <math>30</math> seconds. Then after <math>27 \times 30 = 810</math> seconds (or <math>13 \frac{1}{2}</math> minutes), there are <math>27</math> toys in the box. Mia's mom will then put the remaining <math>3</math> toys into the box after <math>30</math> more seconds, so the total time taken is <math>27\times 30+30=840</math> seconds, or <math>\boxed{(\textbf{B})\ 14}</math> minutes.
 
 
How did you choose to do <math>27\times30?</math>
 
~A question by greenstarwins
 
 
 
==Solution 2==
 
Though Mia's mom places <math>3</math> toys every <math>30</math> seconds, Mia takes out <math>2</math> toys right after. Therefore, after <math>30</math> seconds, the two have collectively placed <math>1</math> toy into the box. Therefore by <math>13.5</math> minutes, the two would have placed <math>27</math> toys into the box. Therefore, at <math>14</math> minutes, the two would have placed <math>30</math> toys into the box. Though Mia may take <math>2</math> toys out right after, the number of toys in the box first reaches <math>30</math> by <math>14</math> minutes. <math>\boxed{(\textbf{B})\ 14}</math>
 
  
 
==Video Solution==
 
==Video Solution==

Latest revision as of 13:13, 3 February 2021

Problem

Mia is "helping" her mom pick up $30$ toys that are strewn on the floor. Mia’s mom manages to put $3$ toys into the toy box every $30$ seconds, but each time immediately after those $30$ seconds have elapsed, Mia takes $2$ toys out of the box. How much time, in minutes, will it take Mia and her mom to put all $30$ toys into the box for the first time?

$\textbf{(A)}\ 13.5\qquad\textbf{(B)}\ 14\qquad\textbf{(C)}\ 14.5\qquad\textbf{(D)}\ 15\qquad\textbf{(E)}\ 15.5$

Solution

Every $30$ seconds, $3$ toys are put in the box and $2$ toys are taken out, so the number of toys increases by $3-2=1$ every $30$ seconds. Then after $27 \times 30 = 810$ seconds (or $13 \frac{1}{2}$ minutes), there are $27$ toys in the box. Mia's mom will then put the remaining $3$ toys into the box after $30$ more seconds, so the total time taken is $27\times 30+30=840$ seconds, or $\boxed{(\textbf{B})\ 14}$ minutes.

Video Solution

https://youtu.be/str7kmcRMY8

https://youtu.be/1F0IB0y6578

~savannahsolver

See also

2017 AMC 10A (ProblemsAnswer KeyResources)
Preceded by
Problem 3
Followed by
Problem 5
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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