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Sequence DS

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Sequence DS

by ithamarsorek » Mon Feb 14, 2011 1:05 pm
I tried to figure out why is this the correct answer but did not come across any satisfactory explanation.


When examining both statements I felt that both can be true. Please help...


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Source: — Data Sufficiency |
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by Night reader » Mon Feb 14, 2011 2:01 pm
st(1) 7-3=4 answer NO, but 11-3=9 answer Yes/Not Sufficient;
st(2) n<6 (5,4,3,2,1); 5=a-2 (a is 7), 4=a-7 (a is 11), 3=a-2 (a is 5), 2=a-11 (a is 13), 1=a-2 (a is 3) Sufficient;

answer B
ithamarsorek wrote:I tried to figure out why is this the correct answer but did not come across any satisfactory explanation.


When examining both statements I felt that both can be true. Please help...


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by ithamarsorek » Mon Feb 14, 2011 2:13 pm
1st part: If they tell me that n is odd, it can be any one of these prime numbers and 2. So why is that incorrect, because it can also be just any of these primes and then it is even?

2nd part: you mean, because we know the range must be less then 6 need to figure which primes under 30 makes n<6 and if there are any? 19-17, 23-19, 3-2, etc... If we find that this kind of #s exist then the statement is correct?

So basically (statement 1 - can be odd or even / no guarantee, statement 2 - must be <6 then we know that those primes are available) ?
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by Night reader » Mon Feb 14, 2011 2:16 pm
yes
ithamarsorek wrote:1st part: If they tell me that n is odd, it can be any one of these prime numbers and 2. So why is that incorrect, because it can also be just any of these primes and then it is even?

2nd part: you mean, because we know the range must be less then 6 need to figure which primes under 30 makes n<6 and if there are any? 19-17, 23-19, 3-2, etc... If we find that this kind of #s exist then the statement is correct?

So basically (statement 1 - can be odd or even / no guarantee, statement 2 - must be <6 then we know that those primes are available) ?
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by gmatmachoman » Mon Feb 14, 2011 10:56 pm
ithamarsorek wrote:I tried to figure out why is this the correct answer but did not come across any satisfactory explanation.


When examining both statements I felt that both can be true. Please help...


Image

It seems the "wordings" in this questions are weird.

St 1 is NOT clear. those numbers can also point to the prime numbers which may not be represented by difference of 2 prime numbers.

For ex" n = 23, now it CAN'T be shown as a difference of 2 prime numbers less than 30.
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