20 x 4 = 4 x 20 by commutativity. But the name of the number 80 is also basically 4 x 20. I guess the English equivalent would be something like ‘what is one thousand times one hundred?’ ‘One hundred thousand because multiplication is commutative’ but that is incredibly unfunny. I guess in English you think of one hundred thousand as being decomposed into a few numbers but maybe in French you just think of quatre-vingts as a single concept and will do a double-take when hearing the reason for the answer before noticing that the name of the number can be decomposed into quatre and vingt. Obviously if the joke was ever funny before it isn’t now.
