53
Subtraction means distance on the number line. From 72 to 100 is 28, and from 100 to 125 is 25. Therefore, 125 - 72 = 28 + 25 = 3 + 25 + 25 = 53. --- Alternately, treat the one's digits separately from the others. 120 - 70 = 50, and 5 - 2 = 3, so 125 - 72 = 53.