1. The problem statement, all variables and given/known data Find P(X>130) where P(X > 130) = 1 − Φ( (130 − µ)/σ ) 2. Relevant equations Φ is the normal distribution density function: http://en.wikipedia.org/wiki/Normal_distribution 3. The attempt at a solution This is pretty simple to use in R if one knew how to. I get a ghastly incorrect answer. Dividing the number of items above 130 by the total number of items yields 0.022, and the above yields something like 0.4e-5 if I use the mean and stdev from the data set. So, what µ and σ are they? They can't be the ones from the data set.