50% increase in x = x + x/2 = 3/2(x)
20% decrease in y = y-y/5 = 4y/5
z= xy^2
Z' = (3x/2)(16y^2/25)
Z' = 24/25 (xy^2)
z - 4%(z) = Z'
SO there was 4% decrease. IMO A.
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z=xy^2 50% increase in X and 20% decrease in Y changes in Z
Source: Beat The GMAT — Problem Solving |
Mani_mba wrote:50% increase in x = x + x/2 = 3/2(x)
20% decrease in y = y-y/5 = 4y/5
z= xy^2
Z' = (3x/2)(16y^2/25)
Z' = 24/25 (xy^2)
1-(24/25)
(25-24)/25
(1/25)*100
4
SO there was 4% decrease. IMO A.
Another way
Original Z = X * Y^2
New x = 1.5x (150% of x i.e 150/100 * x)
New Y = .8Y (80/100*Y)
New Z = 1.5 X * (.8Y) ^ 2
= 1.5 * .64 * X*Y ^2
= .96 * X *Y^2
= 96/100 * X * Y ^ 2
Threfre new Z is 4% reduction of Original Z
Original Z = X * Y^2
New x = 1.5x (150% of x i.e 150/100 * x)
New Y = .8Y (80/100*Y)
New Z = 1.5 X * (.8Y) ^ 2
= 1.5 * .64 * X*Y ^2
= .96 * X *Y^2
= 96/100 * X * Y ^ 2
Threfre new Z is 4% reduction of Original Z
