IPMAT Rohtak Arithmetic > Time & Work PYQs

Two pipes P and Q can fill a tank in $20$ hrs and $25$ hrs respectively while a third pipe R can empty the tank in $30$ hrs. If all the pipes are opened together for $10$ hrs and then pipe R is closed, then in what time the tank can be filled?

Work done by P in one day is double the work done by Q in one day and work done by Q in one day is thrice the work done by R in one day. If P, Q, and R together can complete the work in 30 days, then in how many days P alone can do the work?