SOLUTION: Seth scored an 82%, 88%, and 75% on three tests. What score must he get on the fourth test to bring his average to 80%?
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-> SOLUTION: Seth scored an 82%, 88%, and 75% on three tests. What score must he get on the fourth test to bring his average to 80%?
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You can put this solution on YOUR website! To have an average of 80 on 4 tests, the total of the 4 scores must be 4*80 = 320.
The sum of the three tests he already took is 82+88+75 = 245.
The score he needs on the 4th test is 320-245 = 75.
Or when the numbers being averaged are all close together, as they are in this case, you can solve the problem like this:
1st test: 2 points over the desired average (82-80 = +2)
2nd test: 8 points over the desired average (88-80 = +8)
3rd test: 5 points below the desired average (75-80 = -5)
Cumulatively for the first three tests he is 5 points over the desired average: (+2)+(+8)+(-5) = +5
So on the 4th test, if he wants an average of exactly 80, he has to get a score that is 5 points below that average -- to "balance out" the "extra" 5 points he has going into the 4th test.
And 5 points below 80 is 75.
So again by this method he needs 75 on the 4th test to get an overall average of 80.
With all the word of explanation, it sounds like a lot of work. But the calculations are easier and faster then the first method. Really all you do with this alternate method is this:
