(B) Medians and Quartiles
1. The first quartile (Q1)is a number such that 1 4 of the total number of data that has a value less than the number.
2. The median is the second quartile which is the value that lies at the centre of the data.
3. The third quartile (Q3) is a number such that 3 4of the total number of data that has a value less than the number.
4. The interquartile range is the difference between the third quartile and the first quartile.
Interquartile range = third quartile – first quartile |
Example 2:
![](http://spmmathematics.blog.onlinetuition.com.my/wp-content/uploads/sites/5/2014/09/Picture3.png)
The ogive in the diagram shows the distribution of time (to the nearest second) taken by 100 students in a swimming competition. From the ogive, determine
(a) the median,
(b) the first quartile,
(c) the third quartile
(d) the interquartile range of the time taken.
Solution:
![](http://spmmathematics.blog.onlinetuition.com.my/wp-content/uploads/sites/5/2014/09/Picture4.png)
(d)
Interquartile range
= Third quartile – First quartile
= 54.5 – 44.5
= 10.0 second