SOLUTION: This is my problem. It takes two oil pipelines 30 minutes to fill a tank. One pipeline fills the tank in 45 minutes. How long will it take to fill the tank with the other pipeli

Algebra ->  Algebra  -> Coordinate Systems and Linear Equations  -> Linear Equations and Systems Word Problems -> SOLUTION: This is my problem. It takes two oil pipelines 30 minutes to fill a tank. One pipeline fills the tank in 45 minutes. How long will it take to fill the tank with the other pipeli      Log On

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Question 212323: This is my problem.
It takes two oil pipelines 30 minutes to fill a tank. One pipeline fills the tank in 45 minutes. How long will it take to fill the tank with the other pipeline alone?
I tried this:
x+y=30
y=1.5(x+y)
I got y=-3 and x=33 but it doesn't make since that y=-3. Can you help?
Found 2 solutions by checkley77, Earlsdon:
Answer by checkley77(12569) About Me  (Show Source):
You can put this solution on YOUR website!
XY/(X+Y)=30
45Y/(45+Y)=30
45Y=30(45+Y)
45Y=1,350+30Y
45Y-30Y=1,350
15Y=1,350
Y=1,350/15
Y=90 MINUTES FOR THE SECOND PIPELINE TO FILL THE TANK WORKING ALONE.
PROOF:
45*90/(45+90)=30
4,050/135=30
30=30

Answer by Earlsdon(6103) About Me  (Show Source):
You can put this solution on YOUR website!
If it takes two pipes to fill the tank in 30 minutes, then the two pipelines will fill 1/30 of the tank in one minute.
If it takes one pipeline 45 minutes to fill the tank, the it will fill 1/45 of the tank in one minute.
So subtract:
1%2F30-1%2F45+=+3%2F90-2%2F90 = 1%2F90
So the other pipeline can fill 1/90 of the tank in one minute, therefore it will take 90 minutes to fill the tank.