Answer: There are 4 students in the group.
Step-by-step explanation:
Let the number of students in the group be n
If one of them scored 9 more points , their average score would be 81 points.
So, our equation (1) will be
[tex]\frac{\sum x+9}{n}=81\\\\\sum x+9=81n[/tex]
Similarly,
If one of them scored 3 points less, their average score would be 78 points.
So, our equation (2) will be
[tex]\frac{\sum x-3}{n}=78\\\\\sum x-3=78n[/tex]
So, from equation (1) and (2) we get:
[tex]81n-9=\sum x=78n+3\\\\81n-9=78n+3\\\\81n-78n=3+9\\\\3n=12\\\\n=\frac{12}{3}\\\\n=4[/tex]
Hence, there are 4 students in the group.
