Reading Time: < 1 minute
Last Updated on May 4, 2023
GMAT OFFICIAL GUIDE PS
Solution:
To solve, we use the average equation:
average = sum/quantity
We don’t know the individual scores for each of the first 4 tests, but because their average is 78, we can think of the first 4 scores as 4 scores of 78 each. We then multiply 78 by 4 to get the sum of those four tests:
78 x 4 = 312
Let’s let n = the score on the 5th test. Thus, the sum of the 5 tests is 312 + 5th test score, or 312 + n. Also, because the new average will be 80, we substitute 80 for the new average. We can now solve for n.
Average = sum/quantity
80 = (312 + n)/5
400 = 312 + n
88 = n
Answer: E
