Question: two pipes a and b can fill a tank in 36 hours and 45 hours respectively?
Answer: So Pipes A and B together fill (1/36)+(1/46) = (46+36)/(36*46) or (1/20.19512195)th part of the tank in 1 hour. Hence Pipes A and B together will fill the entire tank in 20.19512195 hours. Given that, Time taken by A is 36 hours and that of b is 45 hours.