reserve tank

(1) zy < 2x^2 – 4xy + 2y^2

okigbo wrote:(1) zy < 2x^2 – 4xy + 2y^2

IS IT a???

Tank 1 Capacity: z gallons.
Filling Rate of Tank 1: (x-y) gallons/min

Time required for Tank 1 to fill to capacity(in minutes): Capacity/Rate = z/(x-y)

Tank 2 Capacity: 2(x-y) gallons [twice the number of gallons of water in Tank1 after one minute]
Filling Rate of Tank 2: y gallons/minute

Time required for Tank 2 to fill to capacity(in minutes): Capacity/Rate = 2(x-y)/y

So, we need to find out if

z/(x-y) > 2(x-y)/y

or, zy > 2(x-y)(x-y)
or, zy > 2x^2 + 2y^2 - 4xy

From (1), zy < 2x2 - 4xy + 2y2 (Assuming it is a minus sign between 2x2 & 4xy)
So this is sufficient.

From (2), 2(x-y) < z/2
or, 4(x-y) < z
or, z > 4(x-y)
or, zy > 4xy - y^2

Not sufficient.

So, IMO the answer should be A.

What is the OA?

Nice work. Didn't even realize this was a standard work problem. OA:A