2017 AMC 8 Problem 14

Attempt Problem 14 of the 2017 AMC 8 below, then check your answer against the video solution and professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2017 AMC 8 solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

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%80\% of the problems she solved alone, but overall 88%88\% of her answers were correct. Zoe had correct answers to 90%90\% of the problems she solved alone. What was Zoe’s overall percentage of correct answers?
89 89
92 92
93 93
96 96
98 98
Answer: C
Concepts:percentage
Small hint:
Assume there are 100100 homework problems to make the percentages concrete.
Big hint:
Use Chloe’s overall score to determine how many jointly solved answers were correct.
Video solution:
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Written solution:
Since the answer is the same regardless of the number of problems, we can assume that there were 100100 problems on the assignment. 80%80\% of 5050 is 40,40, so Chloe answered 4040 questions correctly alone. 88%88\% of 100100 is 88,88, so Chloe answered 8888 questions correctly in total. This means that Chloe answered 88−40=4888 - 40 = 48 together with Zoe.
90%90\% of 5050 is 45,45, so Zoe answered 4545 questions correctly by herself. We know that she answered 4848 questions correctly with Chloe, so she answered 45+48=9345 + 48 = 93 correctly in total. This means that her overall percentage is 93%.93\%.
Thus, C is the correct answer.
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