The present ratio of the ages of Tom and his father is 6 ∶ 10. 8 years ago, the ratio of ages of Tom and his father was 5 ∶ 9. What is the present age of Tom's father?
The present ratio of the ages of Tom and his father is 6 ∶ 10. 8 years ago, the ratio of ages of Tom and his father was 5 ∶ 9. What is the present age of Tom's father? Correct Answer 80
Given:
Present ratio of ages = 6 ∶ 10
The ratio of ages 8 years ago = 5 ∶ 9
Calculation:
Let the present age of Tom and his father be T and F respectively
The present ratio of ages
⇒ T/F = 6/10
⇒ 5T = 3F
⇒ T = 3F/5 ---(i)
The ratio of ages (8 years ago)
⇒ (T - 8)/(F - 8) = 5/9
⇒ 9T - 72 = 5F - 40
Substituting the value of T from equation (i)
⇒ 9 × (3F/5) = 5F + 32
⇒ 27F = 25F + 160
⇒ 2F = 160
⇒ F = 80
∴ The present age of Tom's father is 80 years
Shortcut Trick
Present age of Tom's father = Multiple of 10
Option 1 is not a multiple of 10 thus can be eliminated
Present age of Tom's father - 8 = Multiple of 9
Checking remaining options,
(2) 60 - 8 = 52 (Not a multiple of 9)
(3) 70 - 8 = 62 (Not a multiple of 9)
(4) 80 - 8 = 72 (Multiple of 9)
∵ Only the fourth options satisfy the condition
∴ The present age of Tom's father is 80 years