Question

Four pipes can fill a tank in 70 minutes.how long will it take to fill the tank with 7 pipes are used

Answer 1

Set it up like a ratio:  pipes on the top and minutes on the bottom.  Therefore, your ratio would be 4/70 = 7/x.  Cross-multiply to get 4x=490 and x = 122.5 minutes.  Change that to hours if you'd like by dividing by 60!