The age of a man is twice the sum of the ages of his two sons. Ten years ago, his age was five times the sum of their ages. Find his present age.
a) 40 years
b) 50 years
c) 60 years
d) 70 years​

suppose: the age of the man now is x

the sum of the ages of his two sons now is y

(x, y > 0, x, y € N)

so the age of the man 10 years ago is x - 10

the sum of the ages of his 2 sons ten years ago is

y - 20

because now, The age of a man is twice the sum of the ages of his two sons => x = 2y

because Ten years ago, his age was five times

the sum of their ages

=> x - 10 = 5( y - 20)

<=> x - 10 = 5y - 100

<=> 2x - 20 = 10y - 200

<=> 2x = 2y.5 - 180

but x = 2y => 2x = 5x - 180

<=> 3x = 180

<=> x = 60

=> his present age is 60

72 is the answer to this problem