Question 402276
Let x=amount of time it takes to fill the vat with both pipes open
Then, with both pipes open, the vat fills at the rate of 1/x vat per hr
The inlet pipe fills at the rate of 1/3 vat per hour
The outlet pipe empties at the rate of 1/5 vat per hour
So, with both pipes open the vat fills at the rate of 1/3 - 1/5 =2/15 vat per hour
Now our equation to solve is:
2/15 = 1/x multiply each side by 15x
2x=15
x=7.5 hours time it takes to fill the vat with both pipes open

CK
In 7.5 hours, the inlet pipe fills (1/3)*7.5=2.5 vats
In 7.5 hours the outlet pipe empties (1/5)*7.5=1.5 vats
So, 2.5-1.5=1 vat

Hope this helps---ptaylor