bhumika.k.shah wrote:The point is i get very confused b/w which #s to pick.
How can i kill that phobia , if I must say
Well, first you have to understand your goal in picking numbers.
When we pick numbers on yes/no data sufficiency questions, our aim is to generate both a "yes" and a "no" answer to the original question; accordingly, we try to pick numbers that give us both possible answers.
I say "try" to pick such numbers because here's the #1 rule for picking numbers:
You are only allowed to pick numbers that follow the rules you've been given.
Many people forget this law of DS. We have to treat the information in the stem and the statements as immutable laws of the universe; the only numbers that exist are the ones that follow those laws.
So, reasoning our way through this question:
Is d >= .5?
We think to ourselves: if d < .5, that's a "no" answer; if d >= .5, that's a "yes" answer. If d could be in either range, that's an "insufficient" answer.
(1) d rounded to the nearest tenth is .5.
So, we're only allowed to pick numbers that follow this rule.
First, let's try for a "yes".
If d=.52, then rounded off to the nearest tenth d=.5, so .52 is a permissible number.
Now we plug .52 back into the question:
is .52 >= .5? YES
Since we have a "yes" answer, we now try to generate a "no".
If d=.49, then d rounded off to the nearest tenth is .5, so .49 is a permissible number.
Now we plug .49 back into the question:
is .49 > .5? NO
We have both a yes and a no answer: insufficient; eliminate A and D and move on to (2).
(2) d rounded to the nearest integer is 1.
Well, we could certainly let d=.99, since that gets rounded off to 1.
Is .99>.5? YES
Let's see if we can get a "no" answer as well.
To get a "no" answer, we have to have a value of d less than .5, so let's try a d as big as possible:
d = .499999
When we round .499999 off to the nearest integer, what do we get? 0!
Accordingly, .499999 is NOT a permissible number.
Now, here's where many test takers get confused; this is NOT a "no" answer to the question. On the contrary, we just proved that .49999 is an illegal number and can therefore be ignored.
Since we can't legally pick any numbers that generate a "no" answer, we see that we're definitely getting a "yes" answer to the original question. A definite "yes" = sufficient.
(2) is sufficient, (1) isn't: choose B.
Here's the key takeaway from this question:
Data sufficiency is all about process.
The better you understand how DS works, the fewer mistakes you'll make along the way. If you're struggling with DS, especially on number property yes/no questions (which are, at least conceptually, the most difficult), then slow down and make sure you're following the proper steps.
Even people who are fantastic at math struggle with DS until they understand how it works, so don't rush - take your time until you truly understand what you're doing.
