Question

Week 3 Lecture Notes: Weighted Mean.

1. Let's practice with Weighted Mean calculation.
Give an example of using a weighted mean.
How might it be a better average than a regular mean?

2. Fill in the second column of the table
with any numbers you want.
This column will represent number of students
who had a certain score on a test.

Score	N (weight)
60
70
80
90

Calculate Weighted Mean for the score on this test.

Answer 1

Ans:

1)

Weighted average is required when you are using frequencies or distributions. If you are given a set of data for grades in a math class and you are told that 10 students made a 90, 15 students made an 80, and 5 students made a 70 and asked to determine the average grade for the class, then we cannot use the normal average of (90+80+70)/3. we have to account for the fact that there are multiple instances of each grade.hence, you weight each grade (90, 80, 70) by multiplying it by the number of instances (10, 15, 5 respectively). Then you total the weights and divide by the number of instances to calculate a weighted average.

2)

Score	N (weight)
60	5
70	20
80	25
90	5

Weighted mean=(60*5+70*20+80*25+90*5)/(5+20+25+5)=75.45