Multiply multiples of one hundred

Multiplying three digit multiples of 100 is fairly easy, but there are some addition adjustments to make on some of these.

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To multiply by 21, just multiply by 20 and then add the number on. (To multiply by 20, double and times by 10.)

When multiplying 2-digit numbers by 1-digit in your head usually it is easier to start with the tens.

All these questions are about mentally multiplying by 100 and 1000, including decimals.

Using mental methods to multiply decimals by 10, 100 and 1000.

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