Video: Understanding Inverse Operations to Find the Starting Number

I think of a number. I add 13 to it and then divide by 3. The answer is 12. What number did I think of?

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Video Transcript

I think of a number. I add 13 to it and then divide by three. The answer is 12. What number did I think of?

By letting the number I was thinking of be 𝑥, we can set up an equation. In this example, we firstly added 13 to the number, 𝑥 plus 13. We then divided by three. This gives us 𝑥 plus 13 divided by three. The answer was 12. Therefore, 𝑥 plus 13 divided by three is equal to 12.

In order to solve this equation, we firstly need to multiply both sides by three. This gives us 𝑥 plus 13 is equal to 36, as 12 multiplied by three is 36. Subtracting 13 from both sides of this equation gives us a value of 𝑥 equal to 23. This means that the number I was thinking of initially was 23, as 23 plus 13 divided by three is equal to 12.

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