Compute 49 × 68 in your head

Question

Solve in your head, no paper. What is 49 	imes 68? Aim: under 10 seconds.

Accepted Answer

The closest friendly anchor to 49 is 50, not 100. Round up to 50 and subtract one times the other factor: 49 	imes 68 = 50 	imes 68 - 1 	imes 68 = 3400 - 68 = 3332. 50 	imes 68 is just half of 100 	imes 68 = 6800, so 3400, then knock off 68 to get 3332. Takeaway. The round anchor does not have to be a power of ten: 50 is ideal because 50 	imes n = 	frac{100n}{2}. Always reach for the nearest clean anchor (100, 50, 25, 1000), then correct by the small leftover.

Compute 49 × 68 in your head

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