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Is n an odd number?

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by Max@Math Revolution » Wed Mar 20, 2019 12:31 am

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A

B

C

D

E

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[GMAT math practice question]

Is n an odd number?

1) n and n+2 are prime numbers
2) n+5 is a multiple of 5
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Source: — Data Sufficiency |
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by Max@Math Revolution » Thu Mar 21, 2019 11:16 pm
=>

Forget conventional ways of solving math questions. For DS problems, the VA (Variable Approach) method is the quickest and easiest way to find the answer without actually solving the problem. Remember that equal numbers of variables and independent equations ensure a solution.

The first step of the VA (Variable Approach) method is to modify the original condition and the question. We then recheck the question.

If n and n+2 are prime numbers from condition 1), then both n and n + 2 are odd numbers. Note that 2 is the only even prime number, and 2 + 2 = 4 is not prime.
Thus, condition 1) is sufficient.

Condition 2)
If n + 5 = 10, then n = 5 is an odd number and the answer is 'yes'.
If n + 5 = 15, then n = 10 is an even number and the answer is 'no'.
Thus, condition 2) is not sufficient, since it does not yield a unique solution.

Therefore, A is the answer.
Answer: A
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