Exam average

The average of marks that have on the certificates students of 8A class in mathematics is exactly 2.45. If we did not add 1 and 3 of students Michael and Alena, who arrived a month ago, it would average exactly 2.5.

Determine how many students have class 8A.

Final Answer:

n =  20

Step-by-step explanation:

$$\begin{gathered} 2.45=\frac{S}{n} \\ 2.5=\frac{S-1-3}{n-2} \\ 2.5\cdot (n-2)=S-4 \\ S=2.5\cdot (n-2)+4 \\ 2.45\cdot n=S \\ 2.45\cdot n=2.5\cdot (n-2)+4 \\ 0.05n=1 \\ n=\frac{1}{0.05}=20 \\ n=20 \end{gathered}$$

Try another example