# Histograms

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```					  Histograms                                                    It is important that you can
change fractions to decimals in
• The area of each bar (length  width) is the frequency
order to work out the frequency
density. E.g.
• The frequency density = frequency  class width
1/ = 0.25        3/ = 0.75
4                4
• If the class interval is 25 ≤ x < 30,                         6/                1/ = 0.2
10     = 0.6      5
then the class width = 30 – 25 = 5 etc
7/       = 1.4   14/        = 0.7
5                 20

• Be able to draw a histogram from a grouped frequency table

• Interpret histograms to give very accurate information. This may require you to split a
whole bar on the histogram into a series of equally sized smaller bars. E.g.

If one bar of a histogram represented, say, 40 people, and that bar was then split into
four equally sized vertical bars, then each of the four smaller bars would represent 10 people.
Similarly if the bar representing 40 people was split into ten equally sized vertical bars,
then each of the ten smaller bars would represent 4 people.

• ‘30% weigh more than ……. kg’ is the same as saying ‘70% weigh less than………kg’

```
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