Question 156391
In a particular course a student's semester grade is determined by the average of five hour tests. On her first four hour tests, a student's grades were 82 81 82 and 75. If her semester average turned out to be 82, what did she get on her fifth exam?
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The average 82 is the sum divided by 5. So 82 = sum/5.  Sum = 82*5 = 410.
The other 4 add up to 320, so the 5th one is 410-320, = 90.