In: Statistics and Probability
Fifty cities provided information on vacancy rates (in percent)
for local apartments in the following frequency
distribution.
Vacancy Rate (in percent) | Frequency |
0 up to 3 | 5 |
3 up to 6 | 5 |
6 up to 9 | 10 |
9 up to 12 | 20 |
12 up to 15 | 10 |
a. Calculate the average vacancy rate.
b. Calculate the variance and the standard
deviation for this sample. (Round intermediate calculations
to at least 4 decimal places and final answers to 2 decimal
places.)
Solution:
Given that
Class | Frequency | Mid value | fx | fx2 |
0 - 3 | 5 | 1.5 | 7.5 | 11.25 |
3 - 6 | 5 | 4.5 | 22.5 | 101.25 |
6 - 9 | 10 | 7.5 | 75 | 562.5 |
9 - 12 | 20 | 10.5 | 210 | 2205 |
12 - 15 | 10 | 13.5 | 135 | 1822.5 |
n = 50 | fx = 450 | fx2 = 4702.5 |
Solution:
Given that
a ) The sample mean is
Mean = (fx/ n)
= (450 / 50 )
= 9
The average vacancy rate = 9
b ) The sample variance S2
S2 = (fx2 ) - (( fx )2 / n ) / 1 -n ) * h2
= ( 4702.5 ( ( 450 )2 / 50 ) / 49
= ( 4702.5 - 4050 / 50 ) / 49
= 652.5 / 49
= 13.3163
The sample variance S2 is 13.32
The standard deviation = sample variance
= 13.3163
= 3.6492
The standard deviation = 3.65