SOLUTION: Together, two pipes can fill a tank in 3 hours. If the smaller pipe takes 7 hours to fill the tank, how long does it take the larger pipe to fill the tank?

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Together, two pipes can fill a tank in 3 hours. If the smaller pipe takes 7 hours to fill the tank, how long does it take the larger pipe to fill the tank?       Log On


   

Question 820898: Together, two pipes can fill a tank in 3 hours. If the smaller pipe takes 7 hours to fill the tank, how long does it take the larger pipe to fill the tank?


Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Together, the rate of fil;ling is:
( 1 tank filled ) / ( 3 hrs )
The rate of filling of the smaller pipe is:
( 1 tank filled ) / ( 7 hrs )
-----------------------
Let +t+ = the time in hrs for the larger pipe
to fill the tank
Add the rates of filling of the 2 pipes:
+1%2Ft+%2B+1%2F7+=+1%2F3+
Multiply both sides by +21t+
+21+%2B+3t+=+7t+
+4t+=+21+
+t+=+5.25+ hrs
+.25%2A60+=+15+ min
It will take the larger pipe 5 hrs and 15 min
to fill the tank