If $$M$$ is a sequence of consecutive integers which contains more than 11 terms, what is the average of $$M$$?
>(1) In $$M$$, the number of terms that are less than 10 is equal to the number of terms greater than 21.
>(2) There are 20 terms in $$M$$.

Correct.
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Stat. (1): Since $$M$$ is a set of consecutive integers, it includes all the integers between its smallest and largest terms, including the integers between 10 and 21. Focus on 15.5, the midpoint between 10 and 21. Since the number of terms greater than 21 is equal to the number of terms smaller than 10, the median of $$M$$ (and thus the average) must be 15.5.
If you're not sure, __Plug In__ several sets of integers with equal numbers on either side of the 10–21 interval—the average will always equal 15.5. **Stat.(1) → S → AD**.
Stat. (2): The fact that there are 20 terms in $$M$$ is not __sufficient__ alone
to determine the average, as the terms themselves may vary. Set $$M$$ could
include the set of integers between 1 and 20, inclusive, or the set of
integers between 1,001 and 1,020, inclusive. No single value can be
determined for the average of $$M$$, so **Stat.(2) → IS → A**.

Incorrect.
[[snippet]]
Stat. (1): Since $$M$$ is a set of consecutive integers, it includes all the integers between its smallest and largest terms, including the integers between 10 and 21. Focus on 15.5, the midpoint between 10 and 21. Since the number of terms greater than 21 is equal to the number of terms smaller than 10, the median of $$M$$ (and thus the average) must be 15.5.
If you're not sure, __Plug In__ several sets of integers with equal numbers on either side of the 10–21 interval—the average will always equal 15.5. **Stat.(1) → S → AD**.

Incorrect.
[[snippet]]
Stat. (2): The fact that there are 20 terms in $$M$$ is not __sufficient__ alone
to determine the average, as the terms themselves may vary. Set $$M$$ could
include the set of integers between 1 and 20, inclusive, or the set of
integers between 1,001 and 1,020, inclusive. No single value can be
determined for the average of $$M$$, so **Stat.(2) → IS → ACE**.

Statement (1) ALONE is sufficient, but Statement (2) alone is not sufficient to answer the question asked.

Statement (2) ALONE is sufficient, but Statement (1) alone is not sufficient to answer the question asked.

BOTH Statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient to answer the question asked.

EACH statement ALONE is sufficient to answer the question asked.

Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.