7.3: Percentiles, Quartiles and Interquartile Range

1) Lesson Objectives:

You should be able to 

• find lower quartile, median, upper quartile and percentile from cumulative frequency diagram

Success Criteria:

I am able to 

• find cumulative frequency data

• read from cumulative frequency diagram

Pre-Requisite:

• percentage

Always look through all examples in textbook before lesson.

How to find Quartiles, Percentile and Interquartile Range?

By finding percentage of the total frequency from the vertical axis and reading the ANSWER from the HORIZONTAL AXIS. 

Percentile is a percentage of the total frequency .

Quartiles (is part of a percentile) but it breaks the total frequency into four parts.  It is actually a percentile but in quarters.

Lower Quartile: 

25% of total frequency OR  one quarter of the total frequency OR  0.25 of the total frequency

(25% = 1/4 = 0.25)

Median: 

50% of total frequency OR  half of the total frequency OR  0.5 of the total frequency

(50% = 1/2 = 0.5)

Upper Quartile: 

75% of total frequency OR  three quarter of the total frequency OR  0.75 of the total frequency

(75% = 3/4 = 0.75)

Interquartile Range: (Always read from the horizontal axis to find) 

Answer for Upper Quartile - Lower Quartile