How to multiply in your head: Estimating

How to multiply 321 x 123 in your head.

I’d
convert 321 to 320
convert 123 to 125.

First, I’d do a rough estimate:
I’d say more than 3000. (300 x 100)

If I gotta get closer, I’d add in the lower numbers:
300 * 25 = 750 and 100 * 20 = 200 so 750 + 200 = 950.

3000 + 950 = 3950.

That’d be my estimate.

Kenneth Udut

Here’s how the chinese do it:

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