Joe’s average (arithmetic mean) test score across 4 equally weighted tests was 50. He was allowed to drop his lowest score. After doing so, his average test score improved to 55. What is the lowest test score that was dropped? Choose the correct choice from the following
A) 20
B) 35
C) 55
D) 65
E) 80

Rationale: "the arithmetic mean of 4 equally weighted tests was 50 . so what we can assume is that we have 4 test scores , each 50 . he dropped his lowest score and the avg went to 55 . this means that the lowest score was not 50 and other three scores had given the lowest score 5 each to make it up to 50 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 50 . so the lowest score = 50 - 15 = 35 answer ( b )"
Answer: B