When Mr Bobby is 21 years old, his son is 3 years old. In how many years will he be 4 times as old as his son?
| |
Mr Bobby |
His son |
Difference |
| Before |
21 |
3 |
18 |
| Change |
+ ? |
+ ? |
|
| After |
4 u |
1 u |
3 u |
The difference in the age between Mr Bobby and his son at first and in the end remains the same.
Difference in the age between Mr Bobby and his son
= 4 u - 1 u
= 3 u
3 u = 21 - 3
3 u = 18
1 u = 18 ÷ 3 = 6
Number of years' time so Mr Bobby will be 4 times as old as his son
= 6 - 3
= 3
Answer(s): 3
