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Dispersion (Variance and Standard Deviation) is considered one the most difficult concept.
64 Questions around this concept.
The mean of the numbers and the variance is Then which one of the following gives possible values of ?
The sum of 100 observations and the sum of their squares are 400 and 2475, respectively. Later on, three observations, 3, 4 and 5, were found to be incorrect. If the incorrect observations are omitted, then the variance of the remaining observations is :
Variance and Standard Deviation
The mean of the squares of the deviations from the mean is called the variance and is denoted by σ2 (read as sigma square).
Variance is a quantity which leads to a proper measure of dispersion.
The variance of n observations x1 , x2 ,..., xn is given by
Standard Deviation
The standard deviation is a number that measures how far data values are from their mean.
The positive square-root of the variance is called standard deviation. The standard deviation is usually denoted by σ and it is given by
Variance and Standard Deviation of a Ungrouped Frequency Distribution
The given data is
Variance and Standard deviation of a grouped frequency distribution
The formula for variance and standard deviation are the same as in the case of ungrouped frequency distribution. Here, is the mid point of each class.
Another formula for Standard Deviation
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