SOLUTION: bill's scores on his first four science tests are 86,,90,84,and 91.what test score must bill earn on the fifth test so that his average (mean) will be exactly 88?

Question 641182: bill's scores on his first four science tests are 86,,90,84,and 91.what test score must bill earn on the fifth test so that his average (mean) will be exactly 88?
Answer by josh_jordan(263) (Show Source): You can put this solution on YOUR website!
To solve, we first need to know how to find the average of a group of numbers. To find the average of a group of numbers, you add all the numbers together and divide that answer by the number of numbers you have. For instance, to find the average of 1, 2, 3, 4 and 5, we would add all the numbers together, which would equal 15. We would then divide that number by 5, because there are 5 numbers total: 15/5 = 3. So the average is 3.
Now, to find the average in your problem, we need to look at what we know:
We know there are a total of 5 tests
We know 4 of the scores
The average of all 5 tests is 88
In other words:

If we multiply both sides of this equation by 5, we will get rid of the
fraction, and leave us with:
=

Finally, if we subtract 351 from both sides, we will be left with what x equals, which will be our 5th test score:
=

FINAL ANSWER: Bill must earn an 89 on his fifth test

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