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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 reallife 

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.


We can
therefore plot a graph: · The xaxis (horizontal)
will be Height(m) · The yaxis will (vertical)
will be Cumulative Frequency · We plot the numbers in red · The graph starts at 1.2m,
because this was the lowest value 



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 value We can read this off
the graph to get 1.64m Lower Quartile: On a cumulative
frequency graph we find value We can read this off
the graph to get 1.48m Upper Quartile: On a cumulative
frequency graph we find value We can read this off
the graph to get 1.73m From this we
can deduce the IQR = UQ  LQ =
1.73m1.48m=0.25m 

Histogram – the A/A* graph! Suppose you
are given a table of continuous data (see below). Given a
class eg. the class width is 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 xaxis · Frequency density on the
yaxis 

The next section considers how to read
graphs to find an average 

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


