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This section
looks at a number of the key statistical graphs required for GCSE
Mathematics. It will also
show how you can find averages from a given graph. Being able
to read and then relate the information which a graph shows is an important
skill in real-life |
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Cumulative Frequency Graph If we are
given a table containing continuous data, we can find a running total of the frequency. This is called Cumulative Frequency.
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We can
therefore plot a graph: · The x-axis (horizontal)
will be Height(m) · The y-axis will (vertical)
will be Cumulative Frequency · We plot the numbers in red · The graph starts at 1.2m,
because this was the lowest value
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We can
now use this graph to estimate a number of key values In this case
n=40 (the total number of people Median: On a cumulative frequency
graph we find
We can read this off
the graph to get 1.64m Lower Quartile: On a cumulative
frequency graph we find
We can read this off
the graph to get 1.48m Upper Quartile: On a cumulative
frequency graph we find
We can read this off
the graph to get 1.73m From this we
can deduce the IQR = UQ - LQ =
1.73m-1.48m=0.25m |
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Histogram – the A/A* graph! Suppose you
are given a table of continuous data (see below). Given a
class eg. In the table
below, you can see how the class widths change. In this
case, we will need to construct a histogram to
represent the data. In a
histogram, the AREA of the bars equals the FREQUENCY To achieve this,
we need to calculate a value called the FREQUENCY
DENSITY
We now draw
a graph with: · Height(m) on the x-axis · Frequency density on the
y-axis
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The next section considers how to read
graphs to find an average |
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Finding the mean and median from a
frequency graph A frequency graph to show
the frequency of scores in a test
This graph can be turned into a frequency table
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