2019 AMC 10B Problem 2 — Solution | LIVE by Po-Shen Loh

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2019 AMC 10B Problem 2

Attempt Problem 2 of the 2019 AMC 10B below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 2019 AMC 10B solutions, or check the answer key.

All problems are used with official legal permission of the Mathematical Association of America (MAA).

2.

Consider the statement, "If $n$ is not prime, then $n-2$ is prime." Which of the following values of $n$ is a counterexample to this statement?

$11$

$15$

$19$

$21$

$27$

Answer: E

Concepts:counterexample prime

Difficulty rating: 870

Solution:

We need $n$ to not be prime, so $n$ can only be $15,21,27.$ Then, $n-2$ must be not prime, leaving just $27.$

Thus, the answer is E .

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