Bunuel
The ratio of ages of a father and son is 17:7. 6 years ago the ratio of their ages was 3:1. What is the father's present age?
A. 64
B. 54
C. 51
D. 48
E. 34
I prefer to answer ratio questions using TWO variables.
Let F = the father's age NOW
Let S = the son's age NOW
So, F - 6 = the father's age SIX YEARS AGO
And S - 6 = the son's age SIX YEARS AGO
The ratio of ages of a father and son is (PRESENTLY) 17:7We can write: F/S = 17/7
Cross multiply to get: 7F = 17S
Rewrite as:
7F - 17S = 06 YEARS AGO the ratio of their ages was 3:1We can write: (F-6)/(S-6) = 3/1
Cross multiply to get: (1)(F-6) = (3)(S-6)
Expand to get: F - 6 = 3S - 18
Subtract 3S from both sides: F - 3S - 6 = -18
Add 6 to both sides:
F - 3S = -12What is the father's present age? We have the following equations:
7F - 17S = 0F - 3S = -12Take the bottom equation and multiply both sides by 7 to get:
7F - 17S = 07F - 21S = -84Subtract on the bottom equation from the top equation to get: 4S = 84
Solve: S = 21
So, the son's PRESENT age (S) is
21 years old
Since we already know that F/S = 17/7, we can substitute to get: F/
21 = 17/7
Solve to get: F = 51
Answer: C
Cheers,
Brent