text: exponential distributions? exponential distribution?  if i have the next observations: 5:31 1 ocurrence 5:34 1 oc. 5:36 1 oc. 5:39 1 oc. 5:45 1 oc. what would be the mean? std.dev=mean? how can i get my x from this table? how can i build a frequency table from this information? how can i calculate quartiles with this info?  thank you! i have taken courses in introductory statistics and reliability engineering (which is basically statistics applied to engineering system reliability).  give me a second to grab a few pieces of information and i will get back to you.  ok, an overview of the exponential distribution: the exponential distribution can model processes with a constant occurrence rate (let's call the ocurrence rate "a").  the pdf for the exp. distribution is pdf = a*e^(-a*t) and the cdf = 1-e^(-a*t).  "what would be the mean? std.dev=mean?" both the mean and the standard deviation are equal to 1/(occurrence rate) for the exponential distribution.  mean = std. dev. = 1/a    in your data the ocurrence rate appears to be about (5 ocurrences)/(14 minutes) = 0.36 (ocurrences/minute).  the problem is that the time between ocurrences in your data sample isn't quite evenly spaced, but it is close.   mean = std. dev. = 1/0.36 = 2.8 minutes  "how can i get my x from this table?" i am not sure what x is supposed to represent.  i may have learned a somewhat different notation for this.  "how can i build a frequency table from this information?" a frequency table just shows the number of occurrences in a certain time frame.  so, you can divide up your time intervals into equally spaced bins and see how many occurrences are in each interval.  then make a table out of that.  "how can i calculate quartiles with this info?" i am not sure on this one.