a work as fast as b . if b can complete a work in 12 days independently , the number of days in which a and b can together finish the work in ?
ratio of rates of working of a and b = 2 : 1 ratio of times taken = 1 : 2 a ' s 1 day work = 1 / 6 b ' s 1 day work = 1 / 12 a + b 1 day work = 1 / 6 + 1 / 12 = 3 / 12 = 1 / 4 a and b can finish the work in 4 days answer is c
inverse(add(inverse(12), multiply(const_2, inverse(12))))