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HistogramsHistograms
Objectives:
A Grade Interpret a histogram with unequal class intervals
Prior knowledge:
Draw a Histogram diagram
HistogramsHistograms
Finding Frequencies
0 10 20 30 40 50 60
2
1
Fre
quen
cy d
ensi
ty
Length (cm)
How many lengths are in the class interval 40cm to 60cm?20
1
20 x 1 = 20
How many lengths are in the class interval 30cm to 40cm?10 x 2 = 20
2
10
What is the total frequency? Repeat for the other bars.
10 x 1.5 = 15
20 x 1 = 20
20 + 20 + 20 +15 = 75
75
HistogramsHistograms
From this histogram you could be asked further questions:
0 10 20 30 40 50 60 70
3
2
1
Fre
quen
cy d
ensi
ty
Age (years)
Estimate how many people between the ages of 35 and 55 surf.
Identify the area of the bars to which this applies.
35 55
Remember:frequency is the area
Find the area separately of each bar 5
1.2
15
13
5 × 1.2 = 6 15 × 1 = = 5 3
Estimate of the frequency = 6 + 5 = 11
HistogramsHistograms
Estimate the median from this histogram
110 120 130 140 150 160 170
4
3
2
1
Fre
quen
cy d
ensi
ty
height (cm)
Histogram of children’s heights
Find the total frequency, then find which class interval it is in,draw a line in the bar where the median is represented to find where it is on the x axis
15 × 1 = 15
5 × 3.6 = 18
5 × 3.4 = 17
5 × 4 = 20
10 × 2.5 = 25 10 × 2
= 2010 × 0.5= 5
Frequency 15+18+17+20+25+20+5
= 120
median position= 60
Where is this?
15 33 5060
The median is approximately
137.5 cm