Wiktionary
vulgar fractions
n. (vulgar fraction English)
Usage examples of "vulgar fractions".
That is an easy example in multiplication of vulgar fractions, but, as I daresay you can't do even that, I won't ask you to tell me whether 3/4 X 2 = 1 1/2, but I will ask you to believe me that this was the amount of ear each child was able to lend to the others.