This was posted by Stan Kegel on the groaners listserv. Other mathematical limericks exist (see Google), but this is one of the most straightforward.

Can you figure out this mathematical limerick?

12 + 144 + 20 + (3 x √4)      + (5 X 11) =     9²     +   0
             7

It reads as follows:

A dozen, a gross, and a score
Plus three times the square root of four
      Divided by seven
      Plus five times eleven
Is nine squared, and not a bit more