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

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

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.

Asked on May 18, 2017 in