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求教prep破解ds1 第73题
73. What is the average (arithmetic mean) of eleven consecutive integers?
(1) The average of the first nine integers is 7.
(2) The average of the last nine integers is 9.
答案是D。但是此题并没说数列是递增还是递减的，对于(1),若为递增，则数列为3 4 5 6 7 8 9 10 11 12 13，均值为8； 若为递减的则数列为11 10 9 8 7 6 5 4 3 2 1，均值为6 |
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