Answer to Question #8379 in Statistics and Probability for dustin hanshaw
Find the area under the standard normal curve to the left of z = 1.31
Let X be a random variable which have standard normal distribution, i.e. mean=0, and variance=1. Then the area under the standard normal curve over the interval [a,b] is equal to the probability P(X belongs to [a,b]).
In particular, the area under the standard normal curve to the left some value t is equal to P(X<t)
The function F:R -> R defined by F(t) = P(X<z) is called cummulative probability distruibution and its vaules can be found in almost all books in Probability Theory.
We should find F(1.31). In Excel one can use the function NORMSDIST. Then F(1.31) = P(X<1.31) = NORMSDIST(1.31) = 0.9049