Mr Mark is 2 times as old as his son, David. 21 years ago, the ratio in the age of Mr Mark and David was 7 : 2. Find David's current age.
| |
Mr Mark |
David |
Difference |
| Before |
7x1 =
7 u |
2x1 =
2 u |
5x1 =
5 u |
| Change |
+ 21 |
+ 21 |
|
| After |
2x5 =
10 u |
1x5 =
5 u |
1x5 =
5 u |
The difference in the age of Mr Mark and David at first and in the end remains unchanged. Make the difference in age the same. LCM of 5 and 1 is 5.
The increase in the age of Mr Mark and David is the same.
Increase in David's age
= 5 u - 2 u
= 3 u
3 u = 21
1 u = 21 ÷ 3 = 7
David's current age
= 5 u
= 5 x 7
= 35
Answer(s): 35
