SOLUTION: one pipe can fill a tank in 3 minutes and a second pipe can fill the same tank in 7 minutes. how long will it take the two pipes to fill up this tank together?

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Question 410339: one pipe can fill a tank in 3 minutes and a second pipe can fill the same tank in 7 minutes. how long will it take the two pipes to fill up this tank together?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add the rates of filling:
(1 tank filled/3 min) + (1 tank filled/7 min) = (1 tank filled / x min)
1%2F3+%2B++1%2F7+=+1%2Fx
Multiply both sides by 21x%7D%7D%0D%0A%7B%7B%7B7x+%2B+3x+=+21
10x+=+21
x+=+2.1
both pipes together take 2.1 minutes
check answer:
.3333+%2B+.14286+=+.47619
1%2F2.1+=+.47619
OK