Question about standard deviations? (yeah... maths :( - v quick!)

[Shmee150]

I am really confused, please could somebody enlighten me!

A bottle has mean mass 3kg and standard deviation 0.05kg. What are the mean and standard deviation of 12 bottles?

well mean is 36kg, but I can't for the life of me remember or find out how to do standard deviation of 12 things. Please somebody!

Thank you!

ShMeE

[mike_w]

Standard deviation (if memory serves) is:

For each value, do the value take away the mean. Square the result, and then add them all up, and divide by the number of values. Find the square root of all of that.

I think.

[Shmee150]

I think that's more variance basedm and I'm after something that you do involving 12 and 0.05 and 3, and the answer is 0.173, but I really can't see how to get there.

Anybody else have an idea?

Thanks,

ShMeE

[Byatt]

square your original standard deviation to get the variance

multiply by 12

square root for your new standard deviation

[Shmee150]

Yey!!!!

Thank you very much

ShMeE

[mike_w]

What exactly is the question?

[Shmee150]

The weights of bottles of wine are normally distributed with mean weight 3kg and standard deviation 0.05kg. Find the mean and standard deviation of 12 bottles of wine.

It's about the first question in S3, but it's been a long summer and I can't remember much of what happened in S2

ShMeE