What is the average (arithmetic mean) height of the n people in a certain group?
(1) The average height of the ~$\frac{n}{3}$~ tallest people n the group is 6 feet ~$2\frac{1}{2}$~ inches, and the average height of the rest of the people n the group is 5 feet 10 inches.
(2) The sum of the heights of the n people is 178 feet 9 inches.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
注意n可以被消掉,不能想当然
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