AMC10 2020 A

AMC10 2020 A · Q2

AMC10 2020 A · Q2. It mainly tests Averages (mean).

The numbers 3, 5, 7, $a$, and $b$ have an average (arithmetic mean) of 15. What is the average of $a$ and $b$?

数字3、5、7、$a$和$b$的平均数（算术平均）为15。$a$和$b$的平均数是多少？

(A) 0 0

(B) 15 15

(D) 45 45

(E) 60 60

Answer

Correct choice: (C)

正确答案：（C）

Solution

Because the average of the five numbers is 15, $3 + 5 + 7 + a + b = 5 \cdot 15 = 75$, so $a + b = 75 - (3 + 5 + 7) = 60$. Therefore the average of $a$ and $b$ is $\frac{1}{2}(a+b) = 30$.

因为五个数字的平均数是15，所以$3 + 5 + 7 + a + b = 5 \cdot 15 = 75$，因此$a + b = 75 - (3 + 5 + 7) = 60$。所以$a$和$b$的平均数是$\frac{1}{2}(a+b) = 30$。

Topics

AR.006 Averages (mean)