SOLUTION: Hello there, Here is my problem: A tank can be filled by one pump in 50 minutes and by another pump in 60 minutes. A third pump can drain the tank in 75 minutes. If all 3 pumps go

Question 1053975: Hello there,
Here is my problem: A tank can be filled by one pump in 50 minutes and by another pump in 60 minutes. A third pump can drain the tank in 75 minutes. If all 3 pumps go into operation, how long will it take to fill the tank?
I made a table saying which pumps there are and how long it takes to fill the tank or drain. I keep getting an equation like so:
1/50x + 1/60x - 1/75x = 1
That simplifes to 7/300x = 1
Then x = 42.8571 repeated.
My Online Homework says this answer is wrong. Can you tell me what I am doing wrong?
Thank you!!
Found 2 solutions by josmiceli, ikleyn:
Answer by josmiceli(19441)   (Show Source): You can put this solution on YOUR website!
Add the rates of pumping and subtract the
rate of draining ( as you know )
[ 1 tank filled ] / [ 50 min ]
[ 1 tank filled ] / [ 60 min ]
[ 1 tank drained ] / [ 75 min ]
-----------------------------------------
Let = the time in minutes to fill tank
The rate filling the tank is:
[ 1 tank filled ] / [ t minutes ]
------------------------------

Multiply both sides by

min
Same as your answer -I would start to doubt the
online homework. You might want another opinion also.
Answer by ikleyn(52810)   (Show Source): You can put this solution on YOUR website!
.
For many other similar solved problems on joint work see the lessons
    - Using Fractions to solve word problems on joint work,
    - Solving more complicated word problems on joint work,
    - Selected joint-work word problems from the archive
in this site.

Read them and get be trained in solving joint-work problems.

Also, you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this textbook under the topic "Rate of work and joint work problems" of the section "Word problems".

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