Break It Down

Multiplying 23 x 17 in your head sounds hard. But split it: 23 x 17 = 23 x 10 + 23 x 7 = 230 + 161 = 391. This distributive property turns one hard multiplication into two easy ones.

The key is choosing the best split. Multiplying by 10, 20, or 100 is trivial, so break the harder number into a round part and a small part. 46 x 8 = 40 x 8 + 6 x 8 = 320 + 48 = 368. Each piece fits comfortably in working memory. These are the same splits competitors lean on at the Mental Calculation World Cup.