Everything Maths Grade 10

The box-and-whisker plot shows these five percentiles as in the figure below. The box shows the interquartile
range (the distance betweenQ 1 andQ 3 ). A line inside the box shows the median. The lines extending outside
the box (the whiskers) show where the minimum and maximum values lie. This graph can also be drawn
horizontally.

maximum

upper quartile

median

lower quartile

minimum

( 100 thpercentile)

( 75 thpercentile)

( 50 thpercentile)

( 25 thpercentile)

( 0 thpercentile)

data range interquartile range

VISIT:

This video explains how to draw a box-and-whisker plot for a data set.

See video:2GNCatwww.everythingmaths.co.za

Worked example 14: Five number summary

QUESTION

Draw a box and whisker diagram for the following data set:

f1,25;1,5;2,5;2,5;3,1;3,2;4,1;4,25;4,75;4,8;4,95;5,1g

SOLUTION

Step 1: Determine the minimum and maximum

Since the data set is already sorted, we can read off the minimum as the first value (1,25) and the maximum as

the last value (5,1).

Step 2: Determine the quartiles

There are 12 values in the data set. Using the percentile formula, we can determine that the median lies

between the sixth and seventh values, making it:

3,2+4,1

2

=3,65

The first quartile lies between the third and fourth values, making it:

2,5+2,5

2

=2,5

The third quartile lies between the ninth and tenth values, making it:

4,75+4,8

2

=4,775

Chapter 10. Statistics 379