formulas

#1
Good evening, Ladies and Gents., I am looking for formulas fro the mean, median, quartiles all the above. I have a test this week and my text book hasn't come through the mail as of yet. I'm in need of the formulas only no ex., please. Help:D
 
#4
alkaser266,

Your formula seems to be the median of a r.v with a group frequency distribution. Below is an example:

The following frequency distribution table shows test scores earned
by a group of 671 trainees:

Scores Frequency

45-50 2
50-55 9
55-60 19
60-65 38
65-70 60
70-75 117
75-80 146
80-85 132
85-90 99
90-95 36
95-100 13
Total 671

Define:
L = Lower exact limit of the median class.
nb = Cumulative Frequency of the class preceding the median class
nm = Cumulative Frequency of the median class
i = the width of the median class.
N = the total.

median=L + i*(N/2 - nb)/nm

2+9+19+38+60+117+146=391
Hence the class 75-80 contains the median.

L=75
nb=2+9+19+38+60+117=245
nm=2+9+19+38+60+117+146=391
i=5
N=671

median=L+i*(N/2 - nb)/nm = 75+5*(671/2 - 245)/391
=76.16

The notation is different but it's the same formula.