A student averages 72 on 5 tests. If the lowest score is dropped, the

I like the solution given above. However, you can also treat this as a weighted averages problem, if you don't notice the clever approach with the sums of the scores!

Consider the 72 average as an average of the 4 higher tests, and the 1 lower test.

lowest test ------------------- 72 ------ 4 higher tests

We know that the average of the 4 higher tests is 84, so we can fill that in:

lowest test ------------------- 72 ------ 4 tests averaging 84

The 4 tests that average 84, are 12 points above the overall average. Since there are four of those tests, and only one 'lowest test', the lowest test must be four times further from the average. That means it has to be 4*12 = 48 points below the average.

To find the actual score, figure out what number is 48 points lower than 72. 72-48 = 24. The answer is B.