If yz = 6, what is the value of yz(y - z)?

Question

(1) y*z^2 = -12
(2) y + z = -5

GMATinsight · Answer

Given: yz = 6

Question: Value of yz(y - z)?

Statement 1 : y*z^2 = -12

i.e. y*z*z = -12
i.e. (6)z = -12
i.e. z = -2 i.e. y = -3
SUFFICIENT

Statement 2 : y + z = -5 
Case 1: y=-2 and z=-3
Case 2: y=-3 and z=-2
NOT SUFFICIENT

answer: option A

exc4libur · Answer

(1) y*z^2 = -12   sufic

y=-12/z^2…y>…z>0…yz=6…12/z^2*z=6…12/z=6…z=2…y=3

(2) y + z = -5   insufic

y=-5-z…(-5-z)z=6…-5z-z^2=6…z^2+5z+6=0…(z+2)(z+3)=0 
 (z,y)=(-2,-3)…6(-3-(-2)…6(-3+2)…6(-1)=-6 
 (z,y)=(-3,-2)…6(-2-(-3)…6(-2+3)…6(1)=6

Ans (A)

fauji · Answer

Given: yz = 6
To find: yz(y-z)... we need to find values of y and z.

S1 : y*z^2 = -12
Only possible combination of (y,z) is (-3,-2) ..   Sufficient

S2 : y + z = -5
possible cases of (y,z) are (-2,-3), (-3,-2)
We get different results for yz(y-z), Hence this is   InSufficient

Option A !

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