a person ' s present age is two - fifth of the age of his mother . after 4 years , he will be one - half of the age of his mother . how old is the mother at present ?
"let the mother ' s present age be x years then the person ' s present age = 2 x / 5 ( 2 x / 5 ) + 4 = 1 / 2 ( x + 4 ) 2 ( 2 x + 20 ) = 5 ( x + 4 ) x = 20 answer is c"
divide(subtract(4, add(const_2, const_3)), subtract(divide(const_1, const_2), divide(const_2, add(const_2, const_3))))