Multiply 145 × 12 by splitting the twelve

Question

Twelve splits cleanly into a ten-part and a two-part. Solve in your head. What is 145 	imes 12? Aim: under 8 seconds.

Accepted Answer

Break 12 into 10 + 2 and add the pieces: 145 	imes 12 = 145 	imes 10 + 145 	imes 2 = 1450 + 290 = 1740. So 145 	imes 12 = \mathbf{1740}. The doubling gives 145 	imes 2 = 290, and 1450 + 290 = 1740. A doubling-halving alternative: 145 	imes 12 = 290 	imes 6 = 1740, since 290 	imes 6 = 1740. Either path is quick. Takeaway. Times-12 is "times-10 plus times-2." Splitting a multiplier into a round part and a small part is the workhorse of mental multiplication.

Multiply 145 × 12 by splitting the twelve

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