Question 1131556: The average for Aaron’s test scores must be at least a 90 to earn an a in the class Aaron scored an 87 on the first test and 91 on the second test what scores can Aaron earn on the third test to guarantee at least an a in the class
Answer by greenestamps(13206)   (Show Source):
You can put this solution on YOUR website!
His two test scores so far are 87 and 91, a total of 178.
To get an average of 90 or more on three tests, the sum of the three test scores must be 270 or more.
270-178 = 92; he needs at least a 92 on the third test to average 90 or more and get an A.
Here is a faster and easier way to answer a question like this involving an average of numbers that are all close together: compare each number to the desired average to see where the total lies compared to the average.
In this problem, the desired average is 90. The first score was 87, which is -3 compared to the average; the second score was 91, which is +1 compared to the average. So the first two tests combined are -2 compare to the average.
That means the third score, in order to attain the desired average, must be +2 (at least) compared to the average: 90+2 = 92.
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