Question

I'm thinking of a number. When I multiply by 8 and add –1, I get –17. What's my number?

Answer 1

Say that you're thinking of number
`x`

You multiply it by 8, and have
`8x`

You add -1 (i.e., you subtract 1) and have
`8x-1`

This equals -17, so you have

`8x-1=-17`

Add 1 to both sides

`8x=-16`

Divide both sides by 8:

`x=-2`

So, you were thinking of -2.