Lesson # 2

Purpose:  To learn more terms and look at box and whisker plots.

Grades on the last Algebra test =

There are 15 students in my class.  So, I have 15 test scores.

The median grade (the one in the middle when the grades are written from
smallest to largest) is 84.  There are 7 grades below 84 and 7 grades
above 84.

The median of the
first half of the grades is 72.  This is called the first quartile
mark because there are 3 grades below 72 and 3 grades above 72 but before
the median of 84.

The median of the
second half of the grades is 92.  This is called the third quartile
mark   since one half of the upper range is below this number and one-half of
the upper range is above this number.

More Concepts
1.      Quartiles       =  The regions bounded by the 1st quartile, median, and 3rd quartile marks
of the data.

2.
Interquartile ranges    =  The group of data that is between the 1st and 3rd quartile.
In my example above, the data between 72 and 92 represent 50% of the
data.  This is called the interquartile range.

3.
Box and Whisker Plot   =   Second type of graph to be studied.

For the data mentioned in my class test example;
• The lowest grade was 52.  So, 52 is my left extreme.
• The first quartile mark was 72 (the beginning of my box).  ¼ of the grades  were lower than 72.
• The median grade was 84. ¼ of the grades were between the first quartile mark, 72, and the median grade of 84.
• ½ of the grades are lower than the median mark of 84 and ½ of the grades are higher than the median mark of 84.
• The third quartile grade was 92.  92 is the upper edge of my box. ¼ of the class grades are higher than 92.
• There are whiskers that reach to the extremes from the 1st and 3rd quartiles.

For more examples or instruction, go to Jenn's web site and then return here with your browser back button.