Pipe a can fill a tank in 40 minutes, while pipe b takes 60 minutes to fill the same tank.
if both pipes are used at the same time, how long will it take to fill the tank?

24 minutes.

Step-by-step explanation:

This question shows up in a great many places in math or physics, so it is a pretty good question to learn how to do.

First you should note that answer will be under 40 minutes.

1/40 + 1/60 = 1/TimeTotal

The common denominator on the left is 120 minutes

3/40*3 + 2/60*2 = 1/timetotal

3/120 + 2/120      = 1/ timetotal

5/120 = 1/time total  Now to use to the key stop

What you do now is you always turn the left side over. You do the same thing to total time.

120/5 = total time

24 = total time

What this means is that if you let both pipes run for 24 minutes, they will fill the tank working together.

if you mean

then it's c. 8, -7/3

but if you mean

then it is