Question

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？

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?

$55$

$56$

$57$

$58$

$59$

知识点：平均数

$5$ 个数的总和是 $54 \cdot 5 = 270$ 。前 $2$ 个数的总和是 $48 \cdot 2 = 96$ 。

后 $3$ 个数的总和是 $270 - 96 = 174$ ，所以平均数是 $174 \div 3 = 58$ 。

所以正确答案是 D。

The sum of all $5$ numbers is $54 \cdot 5 = 270.$ The sum of the first $2$ numbers is $48 \cdot 2 = 96.$

The sum of the last $3$ numbers is $270 - 96 = 174.$ The average is therefore $174 \div 3 = 58.$

Thus, D is the correct answer.