Q10 of 108 Page 32

The mean and standard deviation of a group of 100 observations were found to be 20 and 3 respectively. Later on, it was found that three observations were incorrect, which were recorded as 21, 21 and 18. Find the mean and standard deviation if the incorrect observations were omitted.

To Find: Find the correct mean and standard deviation.


Explanation: Here, n=100,


X =




So, Corrected


Corrected


Now, Standard variance = 3


Since, Variance =


Variance = 9


X =


9 =


9 =



Corrected


Corrected


Correct mean =


Corrected Variance =



409.22-400


Corrected variance =9.22


Now, Corrected Standard Deviation =



Correct Deviation is 3.04


Hence, The correct Mean is 20 and Correct SD is 3.04


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