(21) Pipe A can fill a tank in 7 hours, and Pipe B can fill the same tank in 9 hours. Pipe C can empty the tank in 12 hours. If all three pipes are opened simultaneously when the tank is empty, how long will it take to fill the tank completely?
- (a) 6 hours
- (b) 8 hours
- (c) 10 hours
- (d) 12 hours
(22) Pipe A can fill a cistern in 8 hours, and Pipe B can fill the same cistern in 6 hours. Pipe C can empty the cistern in 12 hours. If all three pipes are opened simultaneously when the cistern is empty, how long will it take to fill the cistern completely?
- (a) 4 hours
- (b) 12 hours
- (c) 16 hours
- (d) 24 hours
(23) Pipe A can fill a tank in 6 hours, and Pipe B can fill the same tank in 9 hours. Pipe C can empty the tank in 12 hours. If all three pipes are opened simultaneously when the tank is empty, how long will it take to fill the tank completely?
- (a) 4 hours
- (b) 5 hours
- (c) 8 hours
- (d) 10 hours
(24) Pipe A can fill a tank in 8 hours, and Pipe B can fill the same tank in 12 hours. Pipe C can empty the tank in 16 hours. If all three pipes are opened simultaneously when the tank is empty, how long will it take to fill the tank completely?
- (a) 10 hours
- (b) 12 hours
- (c) 24 hours
- (d) 32 hours
(25) Pipe A can fill a cistern in 10 hours, and Pipe B can fill the same cistern in 15 hours. Pipe C can empty the cistern in 20 hours. If all three pipes are opened simultaneously when the cistern is empty, how long will it take to fill the cistern completely?
- (a) 12 hours
- (b) 20 hours
- (c) 30 hours
- (d) 40 hours
