Bunuel wrote:
Is the integer p divisible by 5 ?
(1) p is divisible by 10.
(2) p is not divisible by 15.
Target question: Is the integer p divisible by 5? Statement 1: p is divisible by 10. If p is divisible by 10, we can write: p = 10k, for some integer k.
Rewrite this as: p = (
5)(2)(k)
This tells us that p is a multiple of
5, which means
p must be divisible by 5Since we can answer the
target question with certainty, statement 1 is SUFFICIENT
Statement 2: p is not divisible by 15.Well, there are MANY numbers that are NOT divisible by 15. Here are two:
Case a: p = 20. In this case, the answer to the target question is
YES, p IS divisible by 5Case b: p = 21. In this case, the answer to the target question is
NO, p is NOT divisible by 5Since we cannot answer the
target question with certainty, statement 2 is NOT SUFFICIENT
Answer: A
Cheers,
Brent
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