Formula to get lower boundary is to subtract the lower class to 0.5.
example:
classes lower boundaries (LB)
46-51 45.5
40-45 39.5
34-39 33.5
28-33 27.5
22-27 21.5
16-21 15.5
10-15 9.5
n=40
you always start in the lower class
10 - 0.5 = 9.5
in quartile:
[tex]qk \frac{kn}{4}[/tex]
Example:
[tex]q3 \: = \frac{3(40)}{4} \\ = \frac{120}{4} \\ = 30[/tex]
