Carlos needs to memorize words on a vocabulary list for French class. He has memorized 30 of the words, which is three-fifths of the list. How many words are on the list?

A neat trick for this problem is that you can easily multiply 3 by a number to make it 30. (3x10=30). using the same number, multiply it by the denominator. 5x10=50. the answer is 50 (3/5 x 10/10 = 30/50 without changing the original ratio)