Given the mean and standard deviation of a normal distribution, find proportions of observations below, above or between given values, find percentiles, find the number of observations in a given range, given the total number of observations. Example: For a given normal distribution, = 20 and = 3. a) Find the proportion of observations that are below 22. b) What proportion of the observations lie between 18 and 22? c) What is the 40th percentile? d) If there are 1200 observations, how many observations are below 19?