1. speed

There are three pipes connecting a large water tank to a pool. Each of the pipes fills the pool at a uniform rate but the rates of different pipes are different. To fill the empty pool, one can open the first pipe for 2 hours and then the second pipe for 1 hour. Also using the second pipe for 2 hours and the thrid pipe for 1 hour fills the empty pool. If the pool is empty and the first pipe was open for 80 minutes, then the second pipe was open for 80 minutes, for how long does the thrid pipe need to be open after that to fill the pool.

You have been given answers for some of your posted questions, and yet you stayed silent afterwards. You don't even acknowlege the answers.

Do you understand the answers?

If you remain silent because you don't undestand them, then, I, for one, find it useless to give you anymore answers.

I did understand the answers, but I didn't know I had to reply to them.

4. the third pipe has to run for 30 min because the fastes pipe is (z) or the third pipe. and then (y) second and then (x) the first one.

z=2y y=2x meaning z=4x

x works for 80 min
y works for 80 min however 80min on y is the same as 40min on x which gives you 2 full hours for x. well y would have to run for another hour but you use the pipe that does the same job in half the time. So 60 divide by 2 equals

30 MIN. good luck!