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READING/DEDUCING MISSING VALUES ON SIMPLE HISTOGRAMS

Suppose you are given the following HISTOGRAM with the y-axis scale missing.

This histogram shows the scores achieved by a year group in a test

 

 

 

 

 

 

 


You are told that 60 people achieved a score between 0 and 20

You can therefore deduce the rest of the missing values using the following steps

KEY FACT: IN A HISTOGRAM, the area of each of the bars EQUALS THE FREQUENCY

       On the histogram above there are six squares representing scores between 0 and 20.

       We know that these six squares represent 60 people

       Therefore each whole square must represent 10 people

We can therefore fill in the following table

 

Score

Area=number of squares

Frequency

(10 per square)

6

60

2+ + =3

30

4

40

+ =1

10

 

We can therefore deduce/answer various questions

Estimate the mean

Find the MEDIAN group