Actual lengths of pregnancy terms for a particular species of mammal are nearly normally distributed about a mean pregnancy length with a standard deviation of 14 days. About what percentage of births would be expected to occur more than 42 days after the mean pregnancy length?
Mean =
Standard deviation, = 14 days
Normal distribution: P(X < A) = P(Z < (A - )/)
Given value of (A - ) = 42
P(a birth occur more than 42 days after the mean pregnancy length) = P(Z > 42/14)
= 1 - P(Z < 42/14)
= 1 - P(Z < 3)
= 1 - 0.9987
= 0.0013
= 0.13%
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