SOLUTION: This is anouther problem that has given me a great deal of trouble. One pipe alone will fill a tank in 7.5 hours. a second pipe will fill it alone in 10 hours. If the second pi

Question 27746: This is anouther problem that has given me a great deal of trouble. One pipe alone will fill a tank in 7.5 hours. a second pipe will fill it alone in 10 hours. If the second pipe were open for 8 hours. And then closed, how long would the frist pipe take to finish filling the tank?
The answer is 1.5 hours, but i don't know how to setup the problem. Thank you.
Answer by Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
One approach to this problem is first find the hourly rate of fill for each pipe. Let's call the first pipe A and the second pipe B.
If pipe A can fill the tank in 7.5 (15/2) hours, then it can fill 2/15 of the tank in 1 hour.
If pipe B can fill the tank in 10 hours, then it can fill 1/10 of the tank in 1 hour.
If pipe B were to be left open for 8 hours, then it would fill 8 X (1/10) of the tank.
So, after 8 hours, 4/5 of the tank would be filled leaving 1/5 of the tank to be filled by pipe A.
Now, pipe A can fill 2/15 of the tank in 1 hour, so how long would it take to fill the 1/5 of the tank?
Divide 1/5 by 2/15 hours.
Pipe A would need 1.5 hours to finish filling the tank.
RELATED QUESTIONS
Hi there, i hope someone could help me solve this problem.. Pls kindly give me a detailed (answered by nerdybill)

Hi! I'm having trouble with my Math homework and I'm hoping that you could answer it.... (answered by ankor@dixie-net.com)

Can you help me solve this word problem? Two pipes can fill a large tank in 10 hours. (answered by ankor@dixie-net.com)

I need help on this problem Two pipes together can fill a tank in 6 hours. Pipe 1 alone (answered by ankor@dixie-net.com)

One pipe can fill a tank in 5 hours, and another pipe can fill a tank in 7 hours. How... (answered by richwmiller)

Pipe A can fill a tank in 4 hours, and pipe B can fill the tank in 3 hours. With the tank (answered by jorel1380)

Pipe A can fill a tank in 8 hours. When both A and pipe B are used th tank is filled in 5 (answered by ankor@dixie-net.com)

Inlet pipes A and B can fill a tank in 6 hours. If the rate of pipe A is twice that of... (answered by josgarithmetic,ikleyn,greenestamps)

3 pipes fill a tank in 0.375 hours. If 2 of them take 1.25 hours and 10/7 hours... (answered by josmiceli)