a and b can do a work in 20 days , b and c can do it in 30 days ; a , b and c together can finish it in 40 days . a and c together will do it in ?
a + b + c 1 day work = 1 / 40 a + b 1 day work = 1 / 20 b + c 1 day work = 1 / 30 a + c 1 day work = 2 * 1 / 40 - 1 / 20 + 1 / 30 = 1 / 30 a and c together will do the work in 30 days . answer is b
inverse(add(subtract(divide(const_1, 30), subtract(divide(const_1, 20), divide(const_1, 40))), subtract(divide(const_1, 20), divide(const_1, 40))))