Question

At a dairy it takes 90 seconds to fill 30 one-gallon jugs of milk. Howmany minutes does it take to fill 90 jugs of milk

Answer 1

90 jugs of milk will take 3 times longer
i.e. 3*90/60 = 270/60 = 27/6 = 4.5 miuntes

Answer 2

90 seconds = 1.5 minutes

1.5 / 30 = x / 90 --(1.5 min to 30 jugs = x min to 90 jugs)
cross multiply
30x = 135
x = 135/30
x = 4.5 minutes