Question

5 years hence the age of jacob will be 3 times that of his son.5 years ago jacob's age was 7 times that of his son. what are their present age?

Answer 1

let's take Jacob's age as X and son's as Y then
$x + 5 = 3(y + 5)$
and
$x - 5 = 7(y - 5)$
then from 1st formula
$x - 3y = 10$
and from 2nd formula
$x - 7y = - 30$
from 3rd and 4th
$4y = 40$
so
$y = 10$
that is Son's age is 10

then from 3rd formula
$x = 10 + 3y$
that is
$x = 40$
Jacob's age is 40