When Mr Andy is 21 years old, his son is 5 years old. In how many years will he be 3 times as old as his son?
| |
Mr Andy |
His son |
Difference |
| Before |
21 |
5 |
16 |
| Change |
+ ? |
+ ? |
|
| After |
3 u |
1 u |
2 u |
The difference in the age between Mr Andy and his son at first and in the end remains the same.
Difference in the age between Mr Andy and his son
= 3 u - 1 u
= 2 u
2 u = 21 - 5
2 u = 16
1 u = 16 ÷ 2 = 8
Number of years' time so Mr Andy will be 3 times as old as his son
= 8 - 5
= 3
Answer(s): 3
