Three people took GMAT practice tests in which the minimum a

What is the maximum possible range of all the scores put together?

Well, it's given in the stem itself: no one scored below 500 or over 750 --> range=250.

This can occur, for example, in the following case: if the scores of the first student were from 500 to 550 (range=50), and the scores of say the second student were from 670 to 750 (range=80), then the range of all the scores put together is (max score) - (min score) = 750 - 500 = 250. Notice that here we can even not consider the third student at all.

What is the minimum possible range of all the scores put together?

This is also given: since the individual range of the third student was 120, then the range of all the scores put together cannot possibly be less than that.

This can occur, for example, in the following case: if the scores of the first student were from 500 to 550 (range=50), the scores of the second student were from 500 to 580 (range=80), and the scores of the third student were from 500 to 620 (range=120), then the range of all the scores put together is (max score) - (min score) = 620 - 500 = 120.

Therefore the difference between the maximum and minimum possible ranges of all their scores put together is 250 - 120 = 130.

Answer: E.

Hope it's clear.