# The birth weights for twins are normally distributed with a mean of 2353 grams and the standard deviation of 647 grams.

answer:

**Answer:-** Most texts use 2 standard deviations as the boundary for usual

verses unusual.

If you convert your mean to a z-score it is 0.

You are looking for the raw score that corresponds to

z= 2 of z=-2

The formula that relates z and x (x is the usual symbol for raw scores) is:

z=(x-u)/sigma

So letting z=2 you get:

2=(x-2353)/647

x-2353=2*647

x=2353+2*647

x=3647

This is the raw score (birth weight) that is 2 standard deviations above the mean.

Then let z=-2

-2=(x-2353)/647

x-2353=-2*647

x=1059

This score is 2 standard deviations below the mean so the answer is **3690.**