Hi architkap,Good instinct: plugging in numbers is a completely valid way to attack a DS question. But there's
one rule that makes or breaks the method, and it's exactly where your test slipped.
Every value you plug in must actually satisfy the statement you're testing. Let's check your two picks against Statement (
1), which says x/|x| < x:
-
x = -1/2: (-1/2)/|-1/2| = -1, and is -1 < -1/2?
Yes. This value is legal, and it gives a YES to "is |x| < 1?"
-
x = 1/2: (1/2)/|1/2| = 1, and is 1 < 1/2?
No. So x = 1/2 does
not obey Statement (
1) at all.
That's the catch. Because x =
1/2 breaks the statement, it can't be used to show anything about Statement (
1). You reached the right final answer, but the "insufficiency" of Statement (
1) wasn't really demonstrated - you got lucky that your surviving case still pointed to C.
The valid pair for Statement (1)To prove Statement (
1) alone is
not sufficient, you need two values that
both satisfy x/|x| < x yet answer the question differently:
-
x = -1/2: obeys (
1), and |x| < 1 -
YES-
x = 2: 2/|2| = 1 < 2 obeys (
1), and |x| < 1 -
NOSame statement, two answers -
not sufficient.
Now bring in Statement (
2), |x| > x, which forces x <
0. That kills the x =
2 case, leaving only negative fractions like -
1/2 - always YES. So together they're
sufficient - C.
Takeaway: in DS, before a test value can "count," confirm it satisfies the statement. Then look for two legal values that disagree.
Answer: Carchitkap
hey, quick question here, below is what I tried to do but not sure if its correct.
From statement 1, I took 2 cases. X as 1/2 and -1/2. I get a yes and no answer. Using statement 2 I know that x is negative. Hence only -1/2 is possible which gives a yes answer to the question.
Is this a correct approach?