1. A variation on mean (or average) is called a Moving Average.  This is used when more data is added at a later date and another average needs to be calculated. (For example sales figures.)  We normally remove the earliest ‘bit’ of data when adding the new ‘bit’ of data. Moving Averages

2. Moving Average The table below shows the quarterly central heating costs, in £’s, at Lucy’s house for the period from 1999 to 2001 Year199920002001 Quarter1 st 2nd3rd4th1st2nd3rd4th1st2nd3rd4th Cost (£)302246122205330266131225351290140248 a)Work out the four-point moving averages for this data. b)Plot the moving averages against time. c)Make comments about trends in the central heating costs.

3. Moving Average Year199920002001 Quarter1 st 2nd3rd4th1st2nd3rd4th1st2nd3rd4th Cost (£)302246122205330266131225351290140248 The first moving average is = 218.75 As we are asked for a 4 point moving average, we average the first 4 values in the first instance. For the next moving average, we add the next 4 figures in line and drop the first value taken.

4. Moving Average The complete list of moving averages is: 218.75, 225.75, 230.75, 257.25, Now to plot these values. No.s 1 to 4No.s 2 to 5No.s 3 to 6No.s 4 to 7 233, 238, 243.25, 249.25, No.s 5 to 8No.s 6 to 9No.s 7 to 10No.s 8 to 11

5. Moving Average Year199920002001 Quarter1 st 2nd3rd4th1st2nd3rd4th1st2nd3rd4th Cost (£)302246122205330266131225351290140248 218.75, 225.75, 230.75, 257.25, 233, 238, 243.25, 249.25, The 1 st moving average occurs at the middle of the 1 st 4 quarters i.e at 2.5. So plot the moving averages at 2.5, 3.5, 4.5, 5.5,etc

6. X = moving averages. The trend line shows a steady increase in fuel costs x x x x x x x x

7. Intermediate Maths Page 415 ex 37.3 No.s 1 – 4

8.  Frequency Polygon This is a type of graph where the frequencies are plotted at the middle of each group and the points joined up by a series of straight lines. Absences (d days) Frequency 0  d  5 4 5  d  10 6 10  d  15 8 15  d  20 5 20  d  25 4 25  d  30 3 Mid point 2.5 7.5 12.5 17.5 22.5 27.5

9. Absences (d days) Frequency 0  d  5 4 5  d  10 6 10  d  15 8 15  d  20 5 20  d  25 4 25  d  30 3 Mid point 2.5 7.5 12.5 17.5 22.5 27.5