Question

A mystery number was decreased by 7, then tripled, followed by two doublings, resulting in thenumber 84. What is the mystery number?

Answer 1

We have:

Let x = mystery number

Then, the number:

decreased by 7, this is equal to x - 7

then tripled, this is 3(x - 7)

followed by two doublings, this is (2)(2)(3)(x - 7)

resulting in the number 84, this is (2)(2)(3)(x - 7) = 84

Therefore, solve x to find the mystery number:

`\begin{gathered} (2)(2)(3)(x-7)=84 \\ 12(x-7)=84 \\ (12(x-7))/(12)=(84)/(12) \\ x-7=7 \\ x-7+7=7+7 \\ x=14 \end{gathered}`

Answer: the mystery number is 14