pipe a that can fill a tank in two hour and pipe b that can fill the tank in an hour are opened simultaneously when the tank is empty . pipe b is shut 30 minutes before the tank overflows . when will the tank overflow ?
the last 30 minutes only pipe a was open . since it needs 2 hour to fill the tank , then in 30 minutes it fills 1 / 4 th of the tank , thus 3 / 4 of the tank is filled with both pipes open . the combined rate of two pipes is 1 + 2 = 3 tanks / hour , therefore to fill 3 / 4 th of the tank they need ( time ) = ( work ) / ( rate ) = ( 3 / 4 ) / 3 = 1 / 4 hours = 15 minutes . total time = 15 + 15 = 30 minutes . answer : e
divide(subtract(const_1, multiply(30, divide(divide(const_1, const_60), const_2))), add(divide(const_1, const_60), divide(divide(const_1, const_60), const_2)))