Simplifying a multiplication by halving and doubling

At times you can see at a glance that a problem can be simplified by halving and doubling. An example is 12×15=6×30. Most people find 6×30 more easy to manage than 12×15.

-If you see that one number being multiplied can be halved to make a simpler number to multiply, try this while doubling the other number being multiplied. If needed, you may be able to do this process over and over until you get the problem more workable.

-If you see that you can take a third, fourth or fifth to make a simpler number, this works also.

-This simplification tool is especially handy in cases where one number can be easily halved while the other number ends in 5. You are then simply multiplying by 10. This brings to mind the rule that to multiply a number by 5, halve the number and add a zero.

Is this simplier?     16×15=8×30     24×25=12×50     14×35=7×70     66×15=33×30    15×12=180

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