Suppose that the distribution of human pregnancies is approximately normal with mean u = 266 days and standard deviation sigma = 16 days

a. what percent of human pregnancies last between 250 and 270 days

b. what percent last less then 280 days

c. what percent last at least 260 days

d. the longest 10% are longer then how many days

e. the shortest 25% are shorter then what number of days

**Solution: **

**a) **Let_{}be the number of day of pregnancy. We need to compute:

_{}

_{}

**b) **We need

_{}

**c)** We need now:

_{}

**d) **We need to find_{}such that

_{}

Using the inverse standard normal distribution we obtain that

_{}

**e) **We need to find_{}such that

_{}

Using the inverse standard normal distribution we obtain that

_{}

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