Question 1094468
<br>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.<br>
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)<br>
Cumulatively for the first three tests he is 5 points over the desired average:  (+2)+(+8)+(-5) = +5<br>
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.<br>
And 5 points below 80 is 75.<br>
So again by this method he needs 75 on the 4th test to get an overall average of 80.<br>
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:<br>
{{{(+2)+(+8)+(-5) = +5}}}  --> the next score should be -5