How long will it take 3 large pipes and 5 small pipes to drain the pond?Nine large pipes will drain the pond in 8 hours and 6 small pipes will...

 Let Pl = volume drained by one large pipe in one
hour

 Let Ps = volume drained by one small pipe in one
hour

 Let t = time

   V - 9P*8 = 0     
                       V-6*p*(16) = 0

  +(-V+6p*16 =
0)                         V = 6*p*16

 -9Pl*8+6ps*16 =
0

   9P*8 = 6p*16                    V-3(P)(t)-5(p)(t) =
0

      P = 1.33p   --------------> 
6p*16-3(1.33p)(t)-5(p)(t) =
0

                                               96p-4pt-5pt =
0

                                                96p =
9pt

                                                 t =
(96p)/(9p)

                                               t = 10.667
hrs = 10 hrs 40 min

==> t= 10 hrs 40
min