Test average

Algebra Level pending

Marvin took eight tests. On the first six tests that he took, he averaged 86.5 points. On the last three tests, he averaged 90 points. If he averaged 87.75 points on all eight tests, how many points did he average on the last two tests?


The answer is 91.5.

A Former Brilliant Member by A Former Brilliant Member

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2 solutions

Richard Costen
Feb 8, 2018

Reading the question carefully, it appears that the 90% average on the last 3 tests is irrelevant to the solution. The total marks for the first 6 tests is 6 × 86.5 = 519 6\times 86.5=519 . The total marks for all 8 tests is 8 × 87.75 = 702 8\times 87.75=702 . Therefore the total for the last 2 tests is 702 − 519 = 183 702 - 519 = 183 . The average is 183 2 = 91.5 \frac{183}{2}=\boxed{91.5} .

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Saya Suka
May 18, 2019

He scored 87 on the sixth test.

Average for the last two tests
= 87.75 + (6 / 2) x (87.75 - 86.5)
= 87.75 + 3 x (1.25)
= 87.75 + 3.75
= 91.5



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