<PRE><B>Question 832173</B>
We use inverse proportion.(the more pipes use the less time use to fill tanks and vise versa.)
Step 1. Write down the ratio in types of term.( no. Of pipes and time/hour)

no. Of pipes             time (hr)
   6                                  1
    4                                  x
Step 2.  Invert one of the ratios. (flip it upside down. Then multiply, divide and solve.

4/6 = 1/x   cross multiply
4x = 6   divide both terms by 4 to get the value of x
x = 6/4 or 1 1/2 hr   

Threfore, it will took 1 1/2 hrs for the 4 pipes to fill the tank w/ same flow</PRE>