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Prime Number Question

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by fangtray » Mon Feb 27, 2012 4:17 pm
Is X a prime number?

1)X is even
2)X cannot be divided evenly by an odd number other than 1.

Ok we know its either BCE because X could be 2, or any other even number

Next, to satisfy #2, X could be 1 or 2, because 3 could be divided by 1 and itself, so any number other than 1 or 2 would not satisfy statement #2.. but 1 is not prime, 2 is prime.

combining, we get C...

but the answer is not C. it's E. What on earth am i missing here, it seems like such an easy question to me.
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Source: — Data Sufficiency |
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by GMATGuruNY » Mon Feb 27, 2012 8:46 pm
fangtray wrote:Is X a prime number?

1)X is even
2)X cannot be divided evenly by an odd number other than 1.

Ok we know its either BCE because X could be 2, or any other even number

Next, to satisfy #2, X could be 1 or 2, because 3 could be divided by 1 and itself, so any number other than 1 or 2 would not satisfy statement #2.. but 1 is not prime, 2 is prime.

combining, we get C...

but the answer is not C. it's E. What on earth am i missing here, it seems like such an easy question to me.
x=2 satisfies both statements: it is even, and its only odd factor is 1.
x=4 satisfies both statements: it is even, and its only odd factor is 1.
Since x=2 is prime and x=4 is not, the two statements combined are INSUFFICIENT.

The correct answer is E.

Any power of 2 satisfies both statements:
x=2³ is even, and its only odd factor is 1.
x=2� is even, and its only odd factor is 1.
x=2� is even, and its only odd factor is 1.
And so on.
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by [email protected] » Tue Feb 28, 2012 4:03 pm
Both the statements are insufficient:

1. If X is even, it can be divided by 2, hence its not a prime number.

2. Think about 8, it cannot be divided by an odd number, but is not a prime number.Think about 10, it can be divided by an odd number, but it is not a prime number. Hence, no conclusion can be reached with this statement.
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by krusta80 » Tue Feb 28, 2012 8:40 pm
[email protected] wrote:Both the statements are insufficient:

1. If X is even, it can be divided by 2, hence its not a prime number.

2. Think about 8, it cannot be divided by an odd number, but is not a prime number.Think about 10, it can be divided by an odd number, but it is not a prime number. Hence, no conclusion can be reached with this statement.
In fact, any power of 2 will work for both cases.
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by bubbliiiiiiii » Thu Mar 01, 2012 4:56 am
I took a different approach.

1)X is even

X could be 2,4,6,8,10 ... (which is both even and odd) - INSUFFICIENT

2)X cannot be divided evenly by an odd number other than 1.
X could be 2,3,4,5,7,8,9,10,11 ... (which is both even and odd) - INSUFFICIENT

Combining 1 and 2,

X could be 2,4,8 .. (which is both even and odd) - INSUFFICIENT
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Pranay
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