Two water tanks, X and Y, were drained simultaneously. If X contains 30 more gallons of water than Y, and both tanks became empty at the same time, how long did it take the tanks to empty?
1. For every gallon drained from Y, 2 gallons drained from X.
2. Tank Y was drained at a constant rate of 20 gallons per hour.
X = Y + 30,
Tx = Ty,
X/Vx = Y/Vy
1. Vx/Vy = 2
2. Vy = 20.
So, neither 1 nor 2 alone is sufficient, but together 1 and 2 are sufficient.