Question

A man who is 42yrs old has a son of 12yrs old in how many years will the father be twice as old as his son?

Answer 1

Let's set the required number of years to `x`

Explanation:

After `x` years the father will be `x+42` years old
The son will then be `x+12` years old

We can now set up the equation:
`x+42=2*(x+12)->`
`x+42=2x+24->`
Now subtract `x` from both sides, and then subtract `24`
`42=x+24->18=x->x=18` years