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# Combining Random Variables Method Needed Watch

1. So I have this question, but I have no idea how to even start...?

It is in the chapter on combining random variables...

The masses of loaves of bread have mean 802g and s.d. of sigma. The probability that a box containing 40 loaves of bread has a mass under 32kg is 0.146. Find the value of sigma.

The answer in the back of the book is 12.0
2. (Original post by Gmart)
So I have this question, but I have no idea how to even start...?

It is in the chapter on combining random variables...

The masses of loaves of bread have mean 802g and s.d. of sigma. The probability that a box containing 40 loaves of bread has a mass under 32kg is 0.146. Find the value of sigma.

The answer in the back of the book is 12.0
X = weight of a loaf of bread
X~N(802, s2), (s=little sigma)

T=X1+X2+X3+...+X40
T~N(40 . 802, 40 . s2)

i.e.
T~(32080,40s2)

P(T<32000) = 0.146

etc etc etc
3. Oh, Ok thanks - I got it

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