A winery has a vat with two pipes leading to it. The inlet pipe can fill the vat in 4 hours, while the outlet pipe can empty it in 10 hours. How long will it take to fill the vat if both pipes are left open?

Question

anonymous · Answer

water filled  in 1 hour by inlet pipe is 1/4
Water emptied by outlet pipe is 1/10
Total water filling the vat in 1 hour is 
1/4 - 1/10
10-4/40  = 6/40

Total time taken to fill the vat is 40/6 = 6 .66 hours 
= 6 hours  and 2/3 *60 minutes  
= 6 hours 40 minutes