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.