When is your birthday V.s. Amount of time since you have seen vector calculus in school?

When is your birthday?	Amount of time since you have seen Vector Calculus in school (triple integrals and such?)
10/24/1985	3 years
3/30	6 years
8/2	1 year
4/19/1983	n years
7/18/1986	27 years
10/19/1982	7 years
8/27/1986	4 years
7/28	5 years
4/24	2 years
12/11/1985	5 years
10/26/88	3 years
12/13/82	8 years
12/6/81	7 years
3,8,81	8 years
18/01/84	4 years
4/8/87	3 years
11/12	never
12/2	3
2/11	-1
7/23	3 yrs
3/21/84	2 years
8/20/86	3 years
8/06/81	10 years
7/28/87	3 years
06/06/69	3 years
07/04/1776	3 years
11/23/86	3

Once again, Great Data!! I am very excited about this data, for multiple reasons. First the question of study when conducting this survey was an attempt to look at the birthday problem. For this size class, I knew we had a high chance (greater than 50%) of having 2 people with the same birthday, but wondered how it would turn out. As you can see above, we do have a match!! You can see that the day of 7/28 occurs twice in the data set. Now I know what your thinking, "what are the chances of that?". Well we can calculate them!! According to wikipedia, the approximate probability of 2 people having the same birthday for a survey of 27 people (n=27) we get:

So we had about a 61.7736% chance of this occurring. I would like to dwell a bit more on the birthdays, but first let's take a look at the right hand column. My point of asking this question on the right was to see how long it has been since they have done the math we are learning in this class. It seams on average we get 4.3 years since people have seen this type of math. (I had to throw out the jokesters giving me too high, like 27, or too low, like -1, and people claiming they had this math "n" years ago.) There seams to be a slight correlation between the amount of people over 25 and having this kinda math 6+ years ago. Which indeed makes sense.

Back to the Left hand column, I wanted to look at when is the most popular month people are born. Let's take a look at a graph from this data!

The graph "shoe's" us that June, July and August have higher birthday yeilds then any other 3 consecutive month combinations. Notice that May and September are completly under represented... or are they?