AMC10 2005 A

AMC10 2005 A · Q6

AMC10 2005 A · Q6. It mainly tests Averages (mean).

The average (mean) of 20 numbers is 30, and the average of 30 other numbers is 20. What is the average of all 50 numbers?

20 个数的平均数（均值）是 30，另外 30 个数的平均数是 20。这 50 个数的平均数是多少？

(A) 23 23

(B) 24 24

(D) 26 26

(E) 27 27

Answer

Correct choice: (B)

正确答案：（B）

Solution

The sum of the 50 numbers is $20 \cdot 30 + 30 \cdot 20 = 1200$. Their average is $1200/50 = 24$.

50 个数的总和是 $20 \cdot 30 + 30 \cdot 20 = 1200$。它们的平均数是 $1200/50 = 24$。

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