Hi,

I've been trying to figure this one out but could really do with some help.

I'm looking to derive the cumulative probability from normal distribution when the mean and standard deviation are known variables. I know i can use the NORMDIST function in excel (which looks like NORMDIST(x,mean,stdev,1[to indicate cumulative]) but i'd like to be able to derive this manually.

E.g. i have a part which fails at a mean of 30,000 hours with a StDev of 5000, if x = 42500 hours what is the cumulative probability?

Thanks