SOLUTION: Pipe A fills a 100 gallon tub at a rate of 10 gallons a minute, Pipe B fills the tub at a rate of 20 gallons a minute, Hole C empties the tub at a rate of 5 gallons a minute,

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Pipe A fills a 100 gallon tub at a rate of 10 gallons a minute, Pipe B fills the tub at a rate of 20 gallons a minute, Hole C empties the tub at a rate of 5 gallons a minute,       Log On


   

Question 885294: Pipe A fills a 100 gallon tub at a rate of 10 gallons a minute,
Pipe B fills the tub at a rate of 20 gallons a minute,
Hole C empties the tub at a rate of 5 gallons a minute,
how many minutes to fill the tub?
This question was in the movie "How Green Was My Valley"
Answer by josgarithmetic(39621) About Me  (Show Source):
You can put this solution on YOUR website!
Uniform rates task or job problem.

Fill 100 gallons is the job to be done. Sum of all the rates gives the effective rate for all of the openings. Rate for hole C is negative!

Rate for all openings at the same time:
%2810%2B20-5%29%28gallons%2Fminute%29=highlight_green%2825%28gallons%2Fminute%29%29.

Next part is to do the 1 job of filling 100 gallons. Find time.
highlight%2825%2At=100%29.
What is t?