AMC 8 2004 Problem 9

AMC8 2004 年第 9 题

统计与数据图表★★☆☆☆

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?

一列 5 个数的平均值为 54。已知前 2 个数的平均值为 48。则最后 3 个数的平均值是多少？

正确答案 · Correct Answer

解析 · Solution

Solution 1

Let the 5 numbers be a, b, c, d, and

e

. Thus

\displaystyle \frac{a+b+c+d+e}{5} = 54

and a+b+c+d+e = 270. Since

\displaystyle \frac{a+b}{2} = 48

, a+b = 96. Substituting back into our original equation, we have 96+c+d+e = 270 and c+d+e = 174. Dividing by 3 gives the average of 58.

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