So, after thinking about it last night...dreaming about it...and then when I got up, I decided the reason I don't feel comfortable with this is because I'm leaving out the fact that the first birthday and the second birthday could be on the same day.
Also, I made a mistake in the upper post. I mean to say 1-the equation I selected.
So I'm going to put what I decided is the final answer here, so if other's google it (I didn't come up with anything) they have some sort of guide, with a caveat, that I could be completely wrong, and this could be a more complex problem and I just don't know how to do it.
So I would guess that the probability actually equals 1- (((selected amount x 2) -1) /365).
i.e. the first problem would be 1-(((40 x 2) -1)/365) = 78.4%
the second would be 1- (((10 x 2) -1)/365) = 94.79%
the third would be 1-(((70 x 2) -1)/365) = 61.92%
If you are worried about doing my home work for me (like maybe these are my home work problems - even though I guarantee they aren't), the problem set is due today, so if you jump in next week or next month, I think it would still do people good to know if this is the right way or wrong way to do it. For myself, my teacher doesn't tell me where I went wrong and how to fix it, just marks it right or wrong, and I can't learn to correct it that way, so I'm hoping eventually someone will remark if this is how you do this type of problem.
This feels like the right way to do it, but perhaps it is more complicated and I just don't know enough to see the extra steps.
Now I'm on to figuring out what would the probability be of any three dates being greater or equal to x days apart. Yippee. I'm thinking since the days are independent this is an addition problem, not a multiplication problem.