Compute 615 × 48 in your head

Question

Solve in your head, no paper. What is 615 	imes 48? Aim: under 20 seconds.

Accepted Answer

Route A, split the big factor. 615 = 600 + 15. - 600 	imes 48 = 28800. - 15 	imes 48 = 720. 28800 + 720 = 29520. Route B, round the small factor up and subtract. 48 = 50 - 2. - 615 	imes 50 = 30750. - 615 	imes 2 = 1230. 30750 - 1230 = 29520. Both land on 29520. Route B is often faster when the 2-digit factor sits just below a multiple of 10 or 25. Takeaway. For 3 	imes 2-digit products, either peel the big factor's round chunk or round the small factor to a nearby multiple of ten and correct. Picking whichever leaves the easier leftover is the whole skill.

Compute 615 × 48 in your head

Your answer

More Mental Math questions