Billy is 5 years old. His father is 42 years older than him. In how many years will Billy's father be 4 times as old as Billy?
| |
His father |
Billy |
Difference |
| Before |
47 |
5 |
42 |
| Change |
+ ? |
+ ? |
|
| After |
4 u |
1 u |
3 u |
The difference in the age between Billy and his father at first and in the end remains the same.
Difference in the age between Billy and his father
= 4 u - 1 u
= 3 u
3 u = 42
1 u = 42 ÷ 3 = 14
The increase in age of Billy and his father remains the same.
Number of years' time so Billy's father will be 4 times as old as Billy
= 14 - 5
= 9
Answer(s): 9
