Standard Deviation

Q. The mean and S.D. of the marks of 200 candidates were found to be 40 and 15 respectively. Later, it was discovered that a score of 40 was wrongly read as 50. The correct mean and S.D. respectively are

1. 39.95, 224.5
2. None the these
3. 14.98, 39.95
4. 39.95, 14.98

Q. In a series of 2n observations, half of them equal a and remaining half equal -a. If the standard deviation of the observations is 2, then |a| equals

1. 
2. 
3. 
4. 2

Q.

If the S.D of a set of observations is 4 and if each observation is divided by 4, the S.D of the new set of observations will be

1. 3
2. 1
3. 2
4. 4

Q.

Which of the following gives a description about standard and mean deviation.

1. measures of dispersion which depends upon the deviations of observations from central tendency

2. maximum and minimum values taken

3. all of the above

4. measures of central tendency of the given observations

Q.

Which of the following can be an alternate representation of variance, where $x_i$ being the midpoint of class intervals, $f_i$ being frequency of class interval and $\overline{x}$ the mean, N = ${\sum }_{i=1}^n{f}_i$

1. 
   

2. 
   

3. 
   

4. 

Q. The variance of first n natural numbers is

1. 
2. 
3. 
4. none of these

Q. If the median and mode of 4 observations is 4, 6 and the sum of squares of observations is 48. Then
standard deviation is

1. 4
2. 
3. 
4. 

Q. A sample of 35 observations has the mean 80 and S.D as 4. A second sample of 65 observations from the same population has mean 70 and S.D. 3. The s.d. of the combined sample is

1. 5.85
2. 5.58
3. none of these
4. 3.42

Q. The S.D. of scores 1, 2, 3, 4, 5 is:

1. 
2. 
3. 
4. 

Q.

The standard deviation of 25 numbers is 40. If each of the numbers is increased by 5, then the new standard deviation will be

1. 40

2. 45

3. $40+\frac{21}{25}$

4. none of these