SOLUTION: "An oil tank is being filled by two pipes. If one of the pipes was used alone it could fill the tank in 15 hours. The second pipe used alone could fill the tank in 12 hours. How lo

Algebra ->  Rate-of-work-word-problems -> SOLUTION: "An oil tank is being filled by two pipes. If one of the pipes was used alone it could fill the tank in 15 hours. The second pipe used alone could fill the tank in 12 hours. How lo      Log On


   

Question 225621: "An oil tank is being filled by two pipes. If one of the pipes was used alone it could fill the tank in 15 hours. The second pipe used alone could fill the tank in 12 hours. How long will it take the two pipes to fill the tank if both are used simultaneously? You must use an algebraic solution. Use on variable to solve this problem. Let x=the number of hours to fill the tank using both pipes."
I just don't even know where to start. I would so appreciate it if you could show me the solution step by step. Thank you!
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
the combined time is less than either individual time

the FRACTION filled by an individual is "combined time"/"individual time"

the FRACTIONS sum to 1, the WHOLE task

let x="combined time"

x/15 + x/12 = 1

multiplying by 60 (LCD) ___ 4x + 5x = 60 ___ 9x = 60

dividing by 60 ___ x = 20/3 = 6hr 40min