SOLUTION: 2 pumps- 1 fills a tank in 5 hours 1 fills a tank in 7 hours-- how many hours to fill the tank with both pumps filling it at the same time? how did you come up with the answer?

Click here to see ALL problems on Rate-of-work-word-problems

Question 99510: 2 pumps-
1 fills a tank in 5 hours
1 fills a tank in 7 hours--
how many hours to fill the tank with both pumps filling it at the same time?
how did you come up with the answer?
thanks...

Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
2 pumps-
1 fills a tank in 5 hours
1 fills a tank in 7 hours--
how many hours to fill the tank with both pumps filling it at the same time?
--------------
1st tank DATA;
Time + 5 hr/job ; Rate = 1/5 job/hr
------------------
2nd tank DATA:
time = 7 hr/job ; Rate = 1/7 job/hr
--------------------------------
Together DATA:
time = x hr/job ; Rate = 1/x job/hr
-----------------------
EQUATION:
rate + rate = together rate
1/5 + 1/7 = 1/x
Multiply thru by 35x to get:
7x + 5x = 35
12x = 35
x = 35/12 = 3 11/12 hr = 3 hr 55 minutes (time to do the job together)
==========================
Cheers,
Stan H.