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题库 / Prep2007E1-DS-52
If the average (arithmetic mean) of four different numbers is 30, how many of the numbers are greater than 30 ?
(1) None of the four numbers is greater than 60.
(2) Two of the four numbers are 9 and 10, respectively.
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.
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不要楼考虑吧第二步
(2)数列里有可能有负数。这样子就会只有1个大于30的数字。
（1）有太多种可能了。
只有（1）和（2）一起才能确保准确数量。