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what is the probability that a randomly slected pregnancy lasts less than 172 days?

The mean being 176 days and the standard deviation being 12

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Kostyantyn M. | Master of MathematicsMaster of Mathematics
4.9 4.9 (36 lesson ratings) (36)
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Assuming that pregnancy lengths are normally distributed (you did not specify - the answer will be different if not), let L be the random variable associated with an individual pregnancy length.
 
Then:
Probability(L < 172) = P((L-176)/12 < (172-176)/12) = P(Z < -1/3) = 0.3694