Question

8 less than 1/3 a number n is -13

Answer 1

Let's set up an equation.

so we know the answer is -13.
1/3 of a number (our variable) can be written as 1/3n.
8 less than that would be subtracting 1/3n by 8

so we have -13 = 1/3n - 8.

To solve:
Add 8 to both sides: -5 = 1/3n
Multiply both sides by 3 (to cancel fraction): -15 = n

You can check by plugging -15 into the equation we made.