Question 644494
The day of a quiz, only Michelle was absent.
 The average grade of the other students was 85.
 When Michelle took a make-up quiz her grade was a 30 which lowered the class
 average to 80. How many students are in the class?
:
Let n = number of students in the class (including Michelle)
:
We know that (n-1) students averaged 85, therefore the equation would be: 
{{{(85(n-1)+30)/n}}} = 80
multiply both sides by n
85(n-1) + 30 = 80n
85n - 85 + 30 = 80n
85n - 55 = 80n
85n - 80n = 55
5n = 55
n = 55/5
n = 11 students in the class
:
:
Check this, find the average
Av = {{{(85(10)+30)/11}}}
Av = 880/11
Av = 80