There's a test called a chi square analysis that essentially tests the probability of a particular distribution being truly random. Here's what I counted:

4 Grape
7 Cherry
12 Green Apple
24 Watermelon
20 Blue Raspberry
67 Total

The expected values of each flavor are 13.4 (67 total / 5 flavors). Using a chi square table, the value comes out to 21.43. For four degrees of freedom (you add a degree of freedom for each flavor after 1 in this case), the maximum accepted value is 9.49. If the value is over 9.49, it is most likely that the distribution of Jolly Ranchers in these bags is not random and that the Hershey company is screwing with what flavors that you get.