Multiplying and dividing by 10 and by 2 are amongst the easiest of calculations to perform.

Here are some calculations that use a combination of these skills:

- To multiply by 5 is the same as to multiply by 10 then divide by 2

Example:

- To multiply by 20 is the same as to mutiply by 10 then multiply by 2, or vice versa

Example:

- To multiply by 25 is the same as to multiply by 100 then divide by 4, or vice versa

Example:

Here’s an applet to practice with.

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