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

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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

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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

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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