Is P – 1 Even?

Question: Is P – 1 even?

1. P is prime
2. P = 2k + 1, when k is a positive integer

1. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
2. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
3. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
4. EACH statement ALONE is sufficient.
5. Statements (1) and (2) TOGETHER are NOT sufficient.

“Is P – 1 even?”- is the topic of GMAT Quantitative reasoning section of GMAT. This question has been taken from the book “GMAT Prep Plus 2021”. GMAT Quant section consists of a total of 31 questions. GMAT Data Sufficiency questions consist of a problem statement followed by two factual statements.GMAT data sufficiency comprise 15 questions which are two-fifths of the total 31 GMAT quant questions.

Answer:

Let’s take statement (1) and evaluate it.

Statement 1 is insufficient by itself because except 2, every prime number is odd.

Now, consider the statement (2) and evaluate it.

This statement is sufficient as it represents a formula for an odd number – any integer becomes odd after it is doubled and then 1 is added to it.

Hence,

Correct Answer: B

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