three pipes of same capacity can fill a tank in 12 hours . if there are only two pipes of same capacity , the tank can be filled in ?
"the part of the tank filled by three pipes in one hour = 1 / 12 = > the part of the tank filled by two pipes in 1 hour = 2 / 3 * 1 / 12 = 1 / 18 . the tank can be filled in 18 hours . answer : a"
inverse(multiply(divide(const_2, const_3), divide(const_1, 12)))