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    Question: "There are 12 numbers in a list. The first 11 numbers have mean 4 and variance 90/11.the 12th number is 7. find the mean and standard deviation of all 12 numbers."

    i found the mean but how do i do the standard deviation?
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    Hey there, you can find the variance of all 12 numbers by expressing the formula as "summation of the first 11 numbers squared" + "the 12th number squared". Have a look at my workings in the image below. Just remember to take the square root of the variance to get the standard deviation, as required by the question

    Name:  variance.jpg
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    (Original post by PetroToxin)
    Hey there, you can find the variance of all 12 numbers by expressing the formula as "summation of the first 11 numbers squared" + "the 12th number squared". Have a look at my workings in the image below. Just remember to take the square root of the variance to get the standard deviation, as required by the question

    Name:  variance.jpg
Views: 16
Size:  422.8 KB
    thank you so much! not seen something like this yet
 
 
 
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