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Bunuel
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Bunuel
Is \(x\) a prime number, given that \(x\) is a positive integer?

(1) \(x^4 > 3000\)
(2) \(x^4 < 10000\)

x is a positive integer

(1) \(x^4 > 3000\) insufic

x=9≠prime, 9^4>3000
x=11=prime, 11^4>3000

(2) \(x^4 < 10000\) insufic

x=9≠prime, 9^4<10000
x=7=prime, 7^4<10000

(1&2) sufic

3000<x^4<10000; primes: 2,3,5,7,11
since, 7^4<3000 and 11^4>10000, then x≠prime

Ans (C)
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For me, I think seeing the algebra visually helps:

First, I think, looking at the two statements, It's pretty suggestive that the answer has to be either C or E.
So, we should be able to put the two statements side by side.

\(3000 > x^4 < 10000\)

This can be rewritten as...

\((3)10^3 > X(X^3) < (10)(10^4)\)

We know at this point that X must be less than 10, but greater than some fourth power of a positive integer.

This narrows down our candidates to {1, 2, ..., 9}

Just as a sanity check, we can see if our highest prime number in that set to the fourth power fits the first condition

\(7^4 < 3000\)

That leaves us with X being either

{8, 9}

Both composite. C.
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