When do you use normalpdf, normalcdf, and invnorm?

normalpdf is a function that returns the probability of a random variable and a single value. You would use this function in order to return the y coordinate on a normal curve. normalcdf is a cumulative distribution function that returns the cumulative probability of the random variable x. invnorm is the inverse normal probability distribution function, it gives the value of x in a probability that is on the left side of the x value.

1: normalpdf pdf = Probability Density Function

This function returns the probability of a single value of the random variable x. Use this to graph a normal curve. Using this function returns the y-coordinates of the normal curve.

Syntax: normalpdf (x, mean, standard deviation)

#2: normalcdf cdf = Cumulative Distribution Function

This function returns the cumulative probability from zero up to some input value of the random variable x. Technically, it returns the percentage of area under a continuous distribution curve from negative infinity to the x. You can, however, set the lower bound.

Syntax: normalcdf (lower bound, upper bound, mean, standard deviation)

#3: invNorm (inv = Inverse Normal Probability Distribution Function

This function returns the x-value given the probability region to the left of the x-value.

(0 < area < 1 must be true.) The inverse normal probability distribution function will find the precise value at a given percent based upon the mean and standard deviation.

Syntax: invNorm (probability, mean, standard deviation)