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#
Cory's average score after 8 tests is 91%. If he gets a 78% on his 9th test, what will his new average be?

8
0
0

A
89.6%
*exact* score on each test, you have to use the information that is given. Since the *average* of all previous scores is 91, assign the score of 91 to each of the 8 previous tests.
This gives us 8 tests with a score of 91 each.
91 \u00D7 8 = 728
To get new average after the 9th test, use the same formula:
$8931_w179_h38.png$
Since there are 2 answer choices that are very close to this, and you don't know which way the .5 will be rounded, extend the division another place by adding a 0 to the dividend, then divide.
You find that the answer is now 89.55, which rounds up to 89.6. Therefore, you now know that 89.5 would *not* be correct. Always extend the decimal places when 2 answer choices are as close as these and you don't know which one is correct.
89.6%

Explaination

The formula for average is:
$4232_w217_h42.png$
For the 8 tests, the average is presented as 91. While we don't know the
B 89.5%

C 90.5%

D 87.5%

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