Two pipes can fill a swimming pool in 15 hours and 20 hours respectively, while the third can empty it in 30 hours. If all the pipes are open simultaneously, then in how many hours the empty swimming pool will be filled?
1
10 hours
2
12 hours
3
15 hours
4
\(15\frac{1}{2}\) hours
5
None of the above/ More than one of the above.