The upper quartile, lower quartile and interquartile discount are £45, £20 and £25 respectively.
Using the graph given:
The upper quartile refers to the 75th percentile of the data . Using the cumulative frequency axis ;
- Upper quartile = 0.75(80) = 60
Cumulative frequency corresponds to a discount of £45
The lower quartile refers to the 25th percentile of the data . Using the cumulative frequency axis ;
- Lower quartile = 0.25(80) = 60
Cumulative frequency corresponds to a discount of £20
The interquartile range is defined as :
- Upper quartile - Lower quartile
Interquartile Range = £45 - £20 = £25