dabral wrote:I find this to be a poorly phrased question because of the use of the word can. I would have written this question in the following manner:
X is a rectangular sheet of glass and Y is a rectangular tabletop, will sheet X completely cover the entire tabletop Y with the edges of sheet X parallel to the edges of the tabletop Y?
(1) The tabletop Y is 36 inches wide by 60 inches long.
(2) The area of one side of the sheet of glass X is 2400 square inches.
Hey dabral!
Phrases like "can", "could", "is it possible" in DS Yes/No problems trip up most people, and it is all about how we think about sufficiency. Here is what I mean, when we see a statement with one of these (like the question above) we often think:
SURE, there are some configurations of LxW that would allow the glass to cover the table so of course it is "possible" so statement (2) must be sufficient but it allows for that possibility (although it isn't a certainty).
But here is what we are missing - while the statements seem to be describing lots of differently shaped sheets of glass or tabletops, they are actually describing a specific sheet of glass and a specific tabletop. The author actually KNOWS whether the sheet of glass will work - he's now giving you descriptions to see if you can figure it out as well. The problem is that he is being too general in his description.
Let me see if I can make this a bit more clear. Let's pretend that we have the following more direct question:
If x is an integer, can x be divided evenly by 3?
Now, the answer to that question will obviously depend on what the real value of x is. So let's pretend to be the question writers and decide on a value for x: x=12. Now it is time to think up some statements - we can write things that describe the number 12 (since we already know what it is) and we can intentionally make some of them too general to be helpful.
How about some of these examples:
(1) x=12
this is pretty obvious and SUPER helpful - this would be sufficient to answer the Q and in fact sufficient to determine exactly the value of X!
(2) x can be divided evenly by 6
well, this isn't as clear as the first one because, while it describes 12, it is pretty general so I can't really determine that x= exactly 12. BUT, I can decide that any number that can be divided evenly by 6 can also be divided evenly by 6's factors (2 and 3) so it would be sufficient. See, I don't have to actually narrow the value of X down to the ACTUAL value to see that (no matter what it happens to be), there is only one way to answer the question. So it is like saying - "hey, I don't know what the real X is that the author is thinking about, BUT, the list of possibilities is short enough, or specific enough, that everything in that lists answers my question in the same way. So no matter what that real value is, I know what answer it will give me!!"
(3) x can be divided evenly by 4
now we see a description of 12 that is as "general" as our example (2) so I certainly can't determine that x= exactly 12. But will this one still be sufficient? If something can be divided evenly by 4, it can be divided evenly by 4's factors (2 and 2) but that doesn't help me with 3. This would be insufficient. WHY? Because I can't narrow down the list of possible x values ENOUGH. In (2), I didn't know the real value of X, BUT I did know that it was part of a list that had the same qualities regarding divisibility by 3. This new list isn't as specific. In the list of numbers that can be divided evenly by 4, some can be divided evenly by 3 (12, 24, 36...) and some cannot (4, 8, 16...). So it now depends on which number I land on to determine the answer to my question. And that is a problem - because there is a real value for X underlying this problem, I just can't narrow down the choices enough to understand more about it.
So here is how I think you should attack DS problems in general (particularly these pesky Yes/No questions). Always assume that there is a specific number or answer to the question you are working on (someone knows it - let's just say the author does). The game of DS is for you to try to FIGURE OUT what the writer already knows. So the writer is giving you hints, trying to "help" you guess the answer he/she already knows. Your job is to determine if the hints are enough for you to get to the same conclusion!
Hope this helps!
Whit
