Three different water pipes P, Q and R working together can fill a tank in 7 hours. After opening for two hours simultaneously, R was closed and P and Q filled the remaining part in 8 hours. Only R can fill the tank in how many hours?
1
18 hours 40 minutes
2
18 hours 10 minutes
3
17 hours 30 minutes
4
16 hours 20 minutes
5
Question Not Attempted