The least common denominator of them is 75:
15, 30, 45, 60, 75, 90, ...
25, 50, 75, 100, ...
Five fifteens fit in 75 and three twenty-fives fit in 75, so we have to multiply the first fraction by 5 and the second one by 3:
10/75
12/75
It means that the second one is bigger by 2/75.
