Is x^2 * y^5 * z>0 ?
s1: --> x,y, z not = 0.
---> if y = -ve, then xz must be -ve so either x or z is -ve.
if y = +ve, then xz must be +ve x and z must be same sign.
consider y = -ve and x=-ve and z = +ve , evaluate question, answer is false.
consider y= -ve and x=+ve and z = -ve, evaluation question, answer is true.
Therefore: s1 not sufficient.
s2: --> either y=-ve and z=+ve OR y=+ve and z=-ve
Ignore x=+ve or x=-ve since there is a x^2 in question
consider y=-ve and z=+ve, evaluation question, answer is false.
consider y=+ve and z=-ve, evaluation question, answer is false.
s2 alone sufficient.
How to quickly see s1 is insufficient?