Question

If I think of a number, double it, and subtract thirteen, I get 17. What number did I think of?

Answer 1

The number that you thought of was 10.

Explanation:

We can represent the number as a variable x, and we can show the operations upon it like this:

"double it"

2x

"subtract 13"

2x - 13

Then, we can set the variable and the operations upon it to 17:

2x - 13 = 17

Finally, we can solve algebraically for x:

2x = 17 + 13

2x = 20

x = 10

So, the number that you thought of was 10.