7 x 13 = 28, according to Abbott & Costello

If you owe 13 weeks of room rent at $7 a week, how much do you owe? According to Abbott and Costello, the answer is not $91. It’s $28. How? Lou Costello “proves” it with three different “math” demonstrations in this version of their classic 7 x 13 = 28 routine.

There are a few different versions of this sketch. This one appears to be from The Abbott and Costello Show, which ran from 1952-1957. The comedy duo’s hot-tempered, cigar-smoking landlord is played by writer and actor Sid Fields.

According to the chorus of YouTube comments for the video, math teachers often share this tricky 7 x 13 = 28 video with their classes. The blogger behind ‘All the Calculations’ explains: “As a teacher, these videos are among my favorites for the shock value and then the discussion about where Abbott and Costello made their mistakes.”

Watch this next: Who’s on First (1953).

Then enjoy a few more math tricks, including: Infinite chocolate: How to create chocolate out of nothing.