Question

1. the average age of 9 students in a class is 25 years. if another student who is 15 years old joins the class, what is the average age of the 10 students?

Explanation:

Step1: Find the total age of 9 students

The formula for the average $\bar{x}=\frac{\sum_{i = 1}^{n}x_{i}}{n}$. Given $n = 9$ and $\bar{x}=25$, then the total age of 9 students $\sum_{i = 1}^{9}x_{i}=n\times\bar{x}=9\times25 = 225$.

Step2: Find the total age of 10 students

A 15 - year - old student joins. So the total age of 10 students is $225+15=240$.

Step3: Calculate the average age of 10 students

Using the average formula again with $n = 10$ and $\sum_{i = 1}^{10}x_{i}=240$, the average age $\bar{x}=\frac{240}{10}=24$.

Answer:

24