posted by K .
ER promises you will be seen in 10 minutes. the standard deviation is 2 minutes. chance someone will wait more than 13 minutes.
i don't know what to do without a population size or sample size
z = (x - mean)/sd
Once you have the z-score, check out a z-table for your probability. (Remember that the problem is looking for "more than 13 minutes" when you determine the probability.)