Question

the list gives the speeds, in miles per hour, of 7 serves made by a professional tennis player. 101, 111, 111, 113, 151, 154, 155 what is the mean speed, in miles per hour, of these 7 serves? a 111 b 113 c 128 d 155

Explanation:

Step1: Calculate the sum of the speeds

$$101 + 111+111 + 113+151+154+155$$
$$=(101 + 111)+111 + 113+(151+154)+155$$
$$=212+111 + 113+305+155$$
$$=(212+111)+113+(305 + 155)$$
$$=323+113+460$$
$$=436+460=896$$

Step2: Calculate the mean

The formula for the mean $\bar{x}=\frac{\sum_{i = 1}^{n}x_{i}}{n}$, where $n = 7$ (the number of data - points) and $\sum_{i=1}^{n}x_{i}=896$.
So, $\bar{x}=\frac{896}{7}=128$

Answer:

C. 128