Question

The mean number of students ill at a school is 3.8 per day, for the first 20 school days of a term. On the 21st day 8 students are ill. What is the mean after 21 days? 

Answer 1

Total for the first 20 days

$\bar x = 3.8$ and $n=20$

$$n \bar x = 20*3.8 =76$$

Total for 21 days

$$\frac{76+8}{21} = 4$$

The mean after 21 days is 4