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# Statistics Question help. watch

1. 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?
2. 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

3. (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

thank you so much! not seen something like this yet

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