Problem: a person ' s present age is one - fifth of the age of his mother . after 8 years , he will be one - half of the age of his mother . how old is the mother at present ?
Rationale: "let the mother ' s present age be x years then the person ' s present age = 2 x / 5 ( 3 x / 5 ) + 8 = 1 / 2 ( x + 8 ) 2 ( 3 x + 40 ) = 5 ( x + 8 ) x = 40 answer is e"
annotated_formula: divide(subtract(8, add(const_2, const_3)), subtract(divide(const_1, const_2), divide(const_2, add(const_2, const_3))))