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Number Prop Set

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Number Prop Set

by yellowho » Fri Jan 28, 2011 8:51 pm
S is a set containing 9 di¤erent positive odd primes. T is a
set containing 8 di¤erent numbers, all of which are members
of S. Which of the following statements CANNOT be true?


(A) The median of S is prime.
(B) The median of T is prime
(C) The median of S is equal to the median of T .
(D) The sum of the terms in S is prime.
(E) The sum of the terms in T is prime.

Can some one explain how you can evaluate B,C,D,E quickly
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by jaxis » Fri Jan 28, 2011 9:52 pm
yellowho,

I think its Option E

Since t has 8 odd primes(sum of even number of odd terms will be even) and

we also know that the sum of the terms of t will be > 2(because the leat possible term in t is 3)

we can say that E is defitely not true(because 2 is the only even prime).Rest of the cases are possible for one or the other combination of odd primes..
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by yellowho » Fri Jan 28, 2011 10:38 pm
You are right. I know on the real test I would've went with the obvious and stop testing. But for the sake of discussion how were you able to eliminate B,C,D quickly. I went from top down.
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by Stuart@KaplanGMAT » Sat Jan 29, 2011 11:46 am
yellowho wrote:You are right. I know on the real test I would've went with the obvious and stop testing. But for the sake of discussion how were you able to eliminate B,C,D quickly. I went from top down.
On the test, you wouldn't want to eliminate them.

You thought of a way to test A quickly, so you dealt with it. If you look at B and think "wow, that's tough, how can I test this", you should temporarily put it aside and move on to the next choice. If you think similarly for C and D and move to E, you'll likely be able to quickly reason that E is impossible.

Here's a key to test day success: you need to control the test, not the other way around.

Accordingly, when faced with annoying and/or time consuming answer choices, only evaluate them if you have no other options. Just because the test maker put answer choice B second on the list doesn't mean that you have to attack it second.
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by yellowho » Sat Jan 29, 2011 9:24 pm
Hi Stuart,

Thanks for the tip. Is there a way to evaluate quickly B,C,D? I just want to be comprehensive and don't want to miss out on concepts.


[quote="Stuart Kovinsky"][quote="yellowho"]You are right. I know on the real test I would've went with the obvious and stop testing. But for the sake of discussion how were you able to eliminate B,C,D quickly. I went from top down.[/quote]

On the test, you wouldn't want to eliminate them.

You thought of a way to test A quickly, so you dealt with it. If you look at B and think "wow, that's tough, how can I test this", you should temporarily put it aside and move on to the next choice. If you think similarly for C and D and move to E, you'll likely be able to quickly reason that E is impossible.

[b]Here's a key to test day success: you need to control the test, not the other way around.[/b]

Accordingly, when faced with annoying and/or time consuming answer choices, only evaluate them if you have no other options. Just because the test maker put answer choice B second on the list doesn't mean that you have to attack it second.[/quote]
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