2019 AMC 8 Problem 7

Below is the video solution and professionally curated solution for Problem 7 of the 2019 AMC 8, from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2019 AMC 8 solutions, or check the answer key.

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Concepts:meanoptimization

Difficulty rating: 960

7.

Shauna takes five tests, each worth a maximum of 100100 points. Her scores on the first three tests are 76,76, 94,94, and 87.87. In order to average 8181 for all five tests, what is the lowest score she could earn on one of the other two tests?

4848

5252

6666

7070

7474

Video solution:
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Written solution:

To minimize one of the scores, we have to maximize the other score. Assume that Shauna gets a 100100 on her fourth test.

The sum of the 44 tests is then 76+94+87+100=357. 76 + 94 + 87 + 100 = 357. For an average of 81,81, Shauna's test scores must add to 581=405.5 \cdot 81 = 405. This means that she needs to get a 405357=48405 - 357 = 48 on her last test.

Thus, the correct answer is A.

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