2. 外语
  3. If the average (arithmetic mean ) of x, y, z, 5 and 7 is 8, which of the following must be true? I. The median of the five num

If the average (arithmetic mean ) of x, y, z, 5 and 7 is 8, which of the following must be true? I. The median of the five num

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问题 If the average (arithmetic mean ) of x, y, z, 5 and 7 is 8, which of the following must be true?
I.   The median of the five numbers cannot be 5.
II.   At least one of x, y, and z is greater than 9.
III.   The range of the five numbers is 2 or more
选项 A、I only
B、II only
C、III only
D、I and III
E、II and III
答案E
解析 若x，y，z，5和7的算术平均值是8，下面哪一个一定正确?
  I．5个数字的中数不能是5。
  II．x，y和z中至少有一个大于9。
  III．5个数字的值域是2或更大。
解：本题的正确答案是(E)。I不对，因为5个数的中数完全可以是5。II一定正确，因为算术平均值为8，则x，y，z中至少有一个大于9。III一定正确，因为x，y，z中至少有1个大于9，那么range至少大于4，2 or more必然满足大于4。
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