Wednesday, September 29, 2010

if x plus y over z is equal to -2, is x positive

if x + y/ z is equal to -2, is x positive?

(1) z is negative
(2) y is positive











TAKEAWAY:
if a problem asks about a certain quantity or variable(s), then you should ISOLATE that quantity or variable(s).


this problem asks a question about x. therefore, you should isolate x.
if you do this, you get x = -y - 2z.

therefore, you have the rephrase you want:
is (-y - 2z) positive?

(1)
insufficient, because we don't know anything about -y (which could be any number at all, and which could definitely be big enough to overwhelm -2z).

(2)
insufficient, because we don't know anything about -2z (which could be any number at all, and which could definitely be big enough to overwhelm -y).

(together)
-y must be negative, but could be ANY negative number.
-2z must be positive, but could be ANY positive number.
the desired sum is therefore (arbitrary pos #) + (arbitrary neg #), which could work out to any number at all.
insufficient.

ans (e)

No comments:

Post a Comment