Question

five years hence the age of jacob will be three times that of his son

Answer 1

Therefore, Present age of Jacob is 40 years and his sons age is 10 years.

Answer 2

Appropriate Question:

Five year hence , the age of Jacob will be three times that of his son. five years ago , Jacob's age was seven times that of his son . what are their present ages ?

Solution :

Let , Present age of Jacob = x years

and Present age of son = y years

From this , we can say that ;

$\sf{}x + 5 = 3(y + 5) \\ \\ \sf{}x + 5 = 3y + 15 \\ \\ \boxed{\sf{}x - 3y - 10 = 0} \: \: \: \: \: \: \: \: \: \: (1) \\ \\ \sf{}x - = 7(y - 5) \\ \\ \sf{}x - 5 = 7y - 35 \\ \\ \boxed{\sf{}x - 7y + 30 = 0} \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: (2) \\ \\ \boxed{ \sf{} x = 3y + 10} \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: (3)$

Putting this value of x from (3) in (2) , we get,

$\sf{}3y + 1 - 7 + 30 = 0 \\ \\ \sf{} - 4y = - 40 \\ \\ \implies{ \sf{}y = 10}$

From (3)

$\sf{}x = 3 \times 10 + 10 \\ \\ \sf{}x = 30 + 10 \\ \\ \sf{}x = 40$

Therefore,

Present age of Jacob = 40 years

Present age of son = 10 years .