Joe’s average (arithmetic mean) test score across 4 equally weighted tests was 90. He was allowed to drop his lowest score. After doing so, his average test score improved to 95. What is the lowest test score that was dropped? Choose the correct choice from the following choices:
A) 20  B) 25  C) 55  D) 75  E) 80

Rationale: "the arithmetic mean of 4 equally weighted tests was 90 . so what we can assume is that we have 4 test scores , each 90 . he dropped his lowest score and the avg went to 95 . this means that the lowest score was not 90 and other three scores had given the lowest score 5 each to make it up to 90 too . when the lowest score was removed , the other 3 scores got their 5 back . so the lowest score was 3 * 5 = 15 less than 90 . so the lowest score = 90 - 15 = 75 answer ( d )"
Answer: D