AMC8 2004
AMC8 2004 · Q9
AMC8 2004 · Q9. It mainly tests Averages (mean).
The average of the five numbers in a list is 54. The average of the first two numbers is 48. What is the average of the last three numbers?
一个列表中五个数的平均数是 54。前两个数的平均数是 48。后三个数的平均数是多少？
(A)
55
55
(B)
56
56
(C)
57
57
(D)
58
58
(E)
59
59
Answer
Correct choice: (D)
正确答案：（D）
Solution
(D) The sum of all five numbers is $5 \times 54 = 270$. The sum of the first two numbers is $2 \times 48 = 96$, so the sum of the last three numbers is $270 - 96 = 174$. The average of the last three numbers is $\frac{174}{3} = 58$.
（D）五个数的总和是 $5 \times 54 = 270$。前两个数的和是 $2 \times 48 = 96$，所以后三个数的和是 $270 - 96 = 174$。后三个数的平均数是 $\frac{174}{3} = 58$。
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