Question

A math club took a math test. Twelve of the members had an average score of 80. Eighteen of the members had an average score of 86. What was the class average?

Answer 1

12 x 80 = 960

18 x 86 = 1548

960 + 1548 = 2508

12 + 18 = 30

2508/30 = 83.6

The class average is 83.6

Answer 2

Class average is 83.6

Explanation:

We are given the following information in the question:

Twelve of the members had an average score of 80. Eighteen of the members had an average score of 86.

Total number of students = 12 + 18 = 30

Formula:

`Mean = \displaystyle\frac{\text{Sum of all marks}}{\text{Total number of students}}`

`Mean = \displaystyle\frac{\text{Sum of all marks of 12 students}}{\text{Total number of students}} \\\\\Rightarrow 80 = \displaystyle\frac{\text{Sum of all marks of 12 students}}{12}\\\\\Rightarrow \text{Sum of all marks of 12 students} = 960`

`Mean = \displaystyle\frac{\text{Sum of all marks of 18 students}}{\text{Total number of students}} \\\\\Rightarrow 86 = \displaystyle\frac{\text{Sum of all marks of 12 students}}{18}\\\\\Rightarrow \text{Sum of all marks of 18 students} = 1548`

Class average =

`\text{Mean} = \displaystyle\frac{\text{Sum of all marks of all students}}{\text{Total number of students}} \\\\ = \displaystyle(960+1548)/(12) = \displaystyle(2508)/(12) = 83.6`

Class average is 83.6