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READING/DEDUCING
MISSING VALUES ON SIMPLE HISTOGRAMS
Suppose you are given the following
HISTOGRAM – with the yaxis 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+ ½ + ½ =3 
30 

4 
40 

½ + ½ =1 
10 
We can therefore deduce/answer various questions
Estimate the mean
Find
the MEDIAN group