Random variables whose range is an interval of real numbers. Section 4.1 Probability Densities For discrete random variables, we used histograms to diagram probability distributions. The sum area of the bars of the histogram represented the probability that a random variable that distribution lies within the specified interval. We have already studied this. Example 1 page 269.
Standard deviation depends on the accuracy of the measuring instruments.
In this example we are assuming that the mean is 1 Kilogram, and the SD is 20 micrograms. X is Normal with mean 0 and SD 20. Use the fact that 10 percent of pop is over 6' tall and the Normal Table to calculate what the standard deviation must be. This is well-approximated by the Normal distribution so again use the Normal table to calculate the answer 8. The exponential distribution models the waiting time until the next arrival of an event in a Poisson process .