two pipes p and q can fill a cistern in 10 and 15 minutes respectively . both are opened together , but at the end of 3 minutes the first is turned off . how much longer will the cistern take to fill ?
"3 / 10 + x / 15 = 1 x = 10 1 / 2 answer : a"
multiply(subtract(const_1, multiply(add(divide(const_1, 10), divide(const_1, 15)), 3)), 15)