Answer:
Step-by-step explanation:
You know that 9 = 10 - 1.
Then 9 of something is equal to 10 of it less one of it. Here, that "something" is four.
[tex]\begin{array}{cl}9\times4&=10\text{ fours}-\boxed{1}\text{ four}\\&=\boxed{40}-4\\&=\boxed{36}\end{array}[/tex]
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Comment on this math
This illustrates a shortcut for multiplying by 9 that can be convenient for mental arithmetic. The idea is to multiply by 10, which just involves adding 0 (or moving the decimal point), then subtract the original number.
