Srivari Riveria is a big housing complex in Coimbatore. Giant tanks are placed in every complex building to cater to the needs of the residents. In a block named Annapurna, three taps P, Q and R can fill a tank in 12, 15 and 30 hours respectively. The caretaker of the complex has instructions to keep tap P open all the time and Q and R are to be opened for one hour alternately. In which hour will the tank in Annapurna become full?