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Measures of Dispersion
What will be the effect of change of origin and change of scale on the standard deviation, mean and variance?
Change of origin and change of scale : Following are the effects of change of origin and change of scale on the mean, standard deviation and variance.
1. Any constant added or substracted (change of origin) than the standard deviation of original data and of change data after addition or substraction will not change but the mean of new data will change.
2. Any constant multiplied or divided (Change of scale) then mean, standard deviation and variation will change of the new changed data.
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Which measure of dispersion is the best and how?
Some measures of dispersion depend upon the spread of values whereas some calculate the variation of values from a central value. Do you agree?
In a town 25% of the persons earned more than Rs. 45000, whereas 75% earned more than Rs. 18000. Calculate the absolute and relative values of dispersion.
A batsman is to be selected for a cricket team. The choice is between X and Y on the basis of their five previous scores which are:
|
X |
Y |
|
25 |
50 |
|
85 |
70 |
|
40 |
65 |
|
80 |
45 |
|
120 |
80 |
Which batsman should be selected if we want
(i) a higher run getter, or
(ii) a more reliable batsman in the team?
To check the quality of two brands of lightbulbs, their life in burning hours was estimated as under for 100 bulbs of each brand.
|
Life (in hrs) |
No. of bulbs |
||
|
Brand A |
Brand B |
||
|
0–50 |
15 |
2 |
|
|
50–100 |
20 |
8 |
|
|
100–150 |
18 |
60 |
|
|
150–200 |
25 |
25 |
|
|
200–250 |
22 |
5 |
|
|
100 |
100 |
||
(i) Which brand gives higher life?
(ii) Which brand is more dependable?Average daily wage of 50 workers of a factory was Rs. 200 with a standard deviation of Rs. 40. Each worker is given a raise of Rs. 20. What is the new average daily wage and standard deviation? Have the wages become more or less uniform?
In the previous question, calculate the relative measures of variation and indicate the value, which in your opinion is more reliable.
If in the previous question, each worker is given a hike of 10% in wages, how are the mean and standard deviation values affected?
The sum of 10 values is 100 and the sum of their squares is 1090. Find the coefficient of variation.
Calculate the mean deviation about mean and standard deviation for the following distribution:
|
Classes |
Frequencies |
|
20–40 |
3 |
|
40–80 |
6 |
|
80–100 |
20 |
|
100–120 |
12 |
|
120–140 |
9 |
|
50 |
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