If we denote the number of students by n , the total sum of all grades is 9.8n . When we exclude the lowest grade of 5, the number of students lowers to n-1 , and the new sum is 9.8n - 5 . With the new average being 10, we can write the equation:
10(n-1) = 9.8n - 5 .
Solving for n :
10n - 10 = 9.8n - 5 ,
10n - 9.8n = 10 - 5 ,
0.2n = 5 ,
n = \frac{5}{0.2} ,
n = 25 ,
n = 25 ,
Hence, the number of students in the class is n=25 .