Question

One third of a number is 12 less than the number itself

Answer 1

Let's say the number is x.

The equation will be:
1/3x + 12 = x
(one third of a number + 12 equals to the number)
Solving the equation:
subtract 1/3x from both sides:
12 = 2/3x
divide by 2
6 = 1/3x
multiply with 3
18 = x

Your number is 18, its one-third is 6, which is 12 less than the number itself.