2017 AMC 8 Problems/Problem 14

Problem 14

Chloe and Zoe are both students in Ms. Demeanor's math class. Last night they each solved half of the problems in their homework assignment alone and then solved the other half together. Chloe had correct answers to only $80\%$ of the problems she solved alone, but overall $88\%$ of her answers were correct. Zoe had correct answers to $90\%$ of the problems she solved alone. What was Zoe's overall percentage of correct answers?

$\textbf{(A) }89\qquad\textbf{(B) }92\qquad\textbf{(C) }93\qquad\textbf{(D) }96\qquad\textbf{(E) }98$

Solution

Let the number of questions that they solved alone be $x$ . Let the percentage of problems they correctly solve together be $a$ %. As given, $\frac{80x}{100} + \frac{ax}{100} = \frac{2 \cdot 88x}{100}$ .

Hence, $a = 96$ .

Zoe got $\frac{90x}{100} + \frac{ax}{100} = \frac{186x}{100}$ problems right out of $2x$ . Therefore, Zoe got $\frac{\frac{186x}{100}}{2x} = \frac{93}{100} = \boxed{\textbf{(C) } 93}$ percent of the problems correct.

Solution 2

Assume the total amount of problems is 200, since we are dealing with percentages, and no values. Then, we know that Chloe got 80 problems correct by herself, and that Chloe got 176 problems right in total. The problems she got right working together, is $176-100$ since she did 100 problems by herself. The problems she got right working together, Zoe also got right.

2017 AMC 8 (Problems • Answer Key • Resources)
Preceded by Problem 13	Followed by Problem 15
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All AJHSME/AMC 8 Problems and Solutions

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2017 AMC 8 Problems/Problem 14

Contents

Problem 14

Solution

Solution 2

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