Question

Please, help me I’m so dumb

Answer 1

Answer:

• 1
• 40
• 36

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.

  $\begin{array}{cl}9\times4&=10\text{ fours}-\boxed{1}\text{ four}\\&=\boxed{40}-4\\&=\boxed{36}\end{array}$

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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.