Question 1176222
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A standard approach:
(1) find the sum of the four scores shown
(2) calculate 91*5, which is the total number of points required for him to have an average of 91 for the five tests
(3) the difference between (1) and (2) is the score he needs to get on the 5th test<br>
An alternative method that is often faster and easier if the numbers being averaged are all "close together":
(1) determine how far over or under the desired average each current score is
(2) add up all those differences
(3) find the score on the 5th test that balances the total from (2)<br>
For this problem....<pre>
1st test: 99  = + 8
2nd test: 86  = - 5
3rd test: 76  = -15
4th test: 95  = + 4
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total:          - 8</pre>
His total scores on the four tests is 8 points below what he needs to get an average of 91; to balance that, his score on the 5th test has to be 8 points above the desired average.<br>
ANSWER: His score on the 5th test must be 91+8=99 to get an average of 91 on the 5 tests.<br>