## A cistern can be completely drained by a pipe in 6 hours. It can be filled by two pipes in 4 hours and 5 hours, respectively. How many hours

A cistern can be completely drained by a pipe in 6 hours. It can be filled by two pipes in 4 hours and 5 hours, respectively. How many hours will the empty cistern take to fill if all the pipes are running?

If x is the time to fill it, which of the following equations could be used to solve for t?

4x + 5x – 6x = 1

15x + 12x – 10x = 60

4x + 5x = 20

## Answers ( No )

x/4 +x/5 -x/6=1

make the denominator the same:

15x/60 +12x/60 -10x/60=1

17x=60

x=60/17=3.53 hours

the second choice is the correct answer.