单选题The average (arithmetic mean) of a set of seven numbers is 81. If one of the numbers is discarded, the average of the remaining numbers is 78. What is the value of the number that was discarded?A98B99C100D101E102
单选题
The average (arithmetic mean) of a set of seven numbers is 81. If one of the numbers is discarded, the average of the remaining numbers is 78. What is the value of the number that was discarded?
A
98
B
99
C
100
D
101
E
102
参考解析
解析：
If the average (arithmetic mean) of a set of seven numbers is 81, then the sum of these seven numbers is 7 x 81 or 567. Since, if one of the numbers is discarded, the average of the six remaining numbers is 78, the sum of these six numbers is 6×78 or 468. Since 567 - 468 = 99, the value of the number that was discarded is 99.
If the average (arithmetic mean) of a set of seven numbers is 81, then the sum of these seven numbers is 7 x 81 or 567. Since, if one of the numbers is discarded, the average of the six remaining numbers is 78, the sum of these six numbers is 6×78 or 468. Since 567 - 468 = 99, the value of the number that was discarded is 99.
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