Bunuel
Is integer p even?
(1) 2p + 1 is odd.
(2) p/2 is even.
Target question: Is integer p even? Statement 1: 2p + 1 = an odd number Some important rules:
#1. ODD +/- ODD = EVEN
#2. ODD +/- EVEN = ODD
#3. EVEN +/- EVEN = EVEN
#4. (ODD)(ODD) = ODD
#5. (ODD)(EVEN) = EVEN
#6. (EVEN)(EVEN) = EVENLet's first subtract 1 from both sides of the equation to get:
2p = (an odd number) - 11 is odd
Since an odd number minus an odd number is even, we can write:
2p = some even numberSince multiplying a number by 2 will turn any number into an even number, statement 1 is not sufficient.
For example, if p = 3, then 2p = 2(3) = 6, which is even. In this case, the answer to the target question is
NO, p is not evenConversely, if p = 4, then 2p = 2(4) = 8, which is even. In this case, the answer to the target question is
YES, p is evenSince we can’t answer the
target question with certainty, statement 1 is NOT SUFFICIENT
Statement 2: p/2 is even Useful property: All even integers can be expressed as 2k, where k is an integerSo, let's rewrite statement 2 as follows:
p/2 = 2k (for some integer k)
Now multiply both sides of the equation by 2 to get:
p = 4kSince 4 is EVEN, we know that 4k will be EVEN for all integer values of k.
In other words, we can be certain of that
p is EVENSince we can answer the
target question with certainty, statement 2 is SUFFICIENT
Answer: B
Cheers,
Brent