Question 1182925: Suppose the age a female has her first period is normally distributed with a mean age of
12 years and standard deviation of 2.5 years.
a. Calculate the probability of randomly selecting a female who will have her first
period after 14 years.
b. Calculate the probability of randomly selecting a female who will have her first
period before 10 years old.
c. Calculate the percentage of females who will have their first period between 12 years
old and 17 years old.
d. A man has a daughter who is now 21 years old and still did not have her first period.
Should he be worried? Explain based on your knowledge of variables that follows a
normal distribution.
Answer by Boreal(15235)   (Show Source):
You can put this solution on YOUR website! z=(x-mean)/sd
>(14-12)/2.5 is z>0.8 with probability 0.2119
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< (10-12)/2.5 is z < -0.8 with same probability of 0.2119
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between 12 and 17, this will be with z between 0 and 2 with probability 0.4772
also 2ndVARS 2 normalcdf(12,17,12,2.5) ENTER
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greater than 21 will be a z>9/2.5 or 3.6 with probability 0.00016. This is very low probability from a statistical standpoint and by age 15 without one a girl has the diagnosis of primary amenorrhea and should be evaluated for hormonal and other issues.
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