10 min
20 min
40 min
50 min
A. 10 min
Workdone by the waste pipe in 1min
=(1/20)-(1/12)+(1/15) = -1/10 [negative sign means emptying]
therefore the waste pipe will empty the full cistern in 10min
100 hrs
122 hrs
177 hrs
112 hrs
7 hrs
7 hrs 30 min
5 hrs
5 hrs 30 min
10 min
20 min
40 min
50 min
18 hrs
13 hrs
20 hrs
23 hrs
39 min
40 min
50 min
45min
20 hrs
23 hrs
30 hrs
21 hrs