Question

Pipe a can fill a tank in 12 hours and pipe b can fill it in 15 hours separately. A third pipe c can empty it in 20 hours.Initially pipe a was opened after one hour pipe b was opened and then after 1 hour when pipe b was opened pipe c was also opened in how many how the tank will be full?

Answer 1

The part of the tank filled in 2 hours =2(1/12)+1(1/15)=7/30
After 2 hours pipe C is open
Three can fill in 1 hour =1/12+1/15-1/20=1/10
The time required to complete remaining part 23/30 is (23/30)10=23/3 hours