# Mean/Variance and Sample SizesWatch

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#1
Im currently studying for my end of year exams and am particuarly struggling with 2 styles of questions. (1 being i cannot find any answers, the other being different wording). I would appreciate it very much if someone could help me and point me in the right direction with either of them. Thanks in advance.

1) A random variable X with a mean of 10 and a standard deviation of 10 is observed. You are interested in the mean and variance of a random variable Y which is a function Y=5X+5
(a) What is the mean of Y?
(b) What is the variance of Y?
(Yes i know it seems easy and i might just be having a moment lol)

2) A random sample of 20 firms is taken with average firm profits of \$60 million and a variance of \$25 million. Which sample size should your survey have at a minimum?
(I have never encountered this style of question without confidence intervals/ levels)
Any help would be appreciated.
0
2 years ago
#2
For the Y-mean sub in X̄ to the equation.

For the Y-variance sub in the variance into the equation BUT ignore the constant.

I've never come across the style of 2 but I'll give it a quick look - I have some ideas in mind
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#3
(Original post by zayn008)
For the Y-mean sub in X̄ to the equation.

For the Y-variance sub in the variance into the equation BUT ignore the constant.

I've never come across the style of 2 but I'll give it a quick look - I have some ideas in mind
Thank you!!
Yeah i've never seen it either.
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