Sean is 20 and his brother is 12. How many years ago was Sean three times as old as his brother?

3(12-x) = 20 - x

Solve for x.

To find out how many years ago Sean was three times as old as his brother, we can set up an equation.

Let's assume the number of years ago is represented by 'x'.

So, 20 - x would be Sean's age 'x' years ago.
And 12 - x would be his brother's age 'x' years ago.

According to the problem, Sean was three times as old as his brother 'x' years ago. So, we can write the equation as:

20 - x = 3(12 - x)

Now, let's solve this equation to find the value of 'x'.

Expanding the equation:

20 - x = 36 - 3x

Combining like terms:

2x - x = 36 - 20

Simplifying:

x = 16

Therefore, 16 years ago, Sean was three times as old as his brother.