Five years ago, a father was 3 times as old as his son, now their...

JAMB 1978

Five years ago, a father was 3 times as old as his son, now their combined ages amount to 110years. thus, the present age of the father is

A. 75 years
B. 60 years
C. 98 years
D. 80 years
E. 105 years

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Correct Answer: Option D

Explanation

Let the present ages of father be x and son = y

five years ago, father = x - 5

son = y - 5

x - 5 = 3(y - 5)

x - 5 = 3y - 15

x - 3y = -15 + 5 = -10 ......(i)

x + y = 110......(ii)

eqn(ii) - eqn(i)

4y = 120

y = 30

sub for y = 30 in eqn(i)

x -10 = 3(30)

x -10 = 90

x = 80