Pipe P and Q can fill a tank in 10 and 12 hours respectively and C can empty it in 6 hours. If all the three are opened at 7 am, at what time will one-fourth of the tank be filled?

[A]10 am

[B]11 am

[C]10 pm

[D]11 pm

**10 pm**

Part of tank filled in 1 hour when all three pipes are opened

∴ The tank will be filled in 60 hours.

∴ One fourth of the tank will be filled in 15 hours so the tank will be filled at 10 pm.

Hence option [C] is correct answer.