The length of horses pregnancies is approximately normally d

The length of horses pregnancies is approximately normally distributed with mean 366-days and standard deviation of 10 days. What is the probability that a randomly chosen pregnancies has gestation period of 360 days or more

Solution

We first get the z score for the critical value. As z = (x - u) / s, then as          
          
x = critical value =    360      
u = mean =    366      
          
s = standard deviation =    10      
          
Thus,          
          
z = (x - u) / s =    -0.6      
          
Thus, using a table/technology, the right tailed area of this is          
          
P(z >   -0.6   ) =    0.725746882 [answer]