Wednesday, June 24, 2009

Practice problems for frequency tables

x___f(x)
20__5
19__6
18__7
17__6
16__4
15__4
14__3
13__2
12__1
11__2

Using this data set written as a frequency table, find the average x-bar, n, the median and the mode.

Answers in the comments.
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1 comment:

Prof. Hubbard said...

n is the sum of the frequencies.

n5+6+7+6+4+4+3+2+1+2 = 40

x-bar is the sum of all the entries divided by n, so we need to multiply the x values by the corresponding f(x) values, then add those values up, then divide by 40.

20*5=100
19*6=114
18*7=126
17*6=102
16*4= 64
15*4= 60
14*3= 42
13*2= 26
12*1= 12
11*2= 22

sum=668

avg=16.7

mode=18, the most frequent value

median is the average of the entries in the 20th and 21st positions

20 in positions 1-5
19 in positions 6-11
18 in positions 12-18
17 in positions 19-24
...
This means 17 is the value in both positions 20 and 21, so 17 is the median value.

June 24, 2009 at 8:46 PM

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