Common sense is useless in science!

[Tiberius]

Great video.

You the Adrian from Athiest Blogger?

If so, your blog rocks.

I am. Thanks for the kind words

About that birthday thing:

365 days in the year
30 people in the class
1/2 chance of 2 people sharing a birthday?

I can't figure that one out.

It's known as the "Birthday paradox", but the math is quite simple. It's easier to do in reverse. Suppose that we wanted to calculate the chances that 2 people did not have the same birthday.

If you have one person in the room, they have a 365/365 chance of not sharing a birthday (since there are no others in the room). If you add another person, they have 364/365 chance of not sharing a birthday (since there are only 364 days left that are not already taken.

If you have 30 people in the room, the calculation looks like this:

365/365 * 364/365 * 363/365 * 362/365 * 361/365 * 360/365 * 359/365 * 358/365 * 357/365 * 356/365 * 355/365 * 354/365 * 353/365 * 352/365 * 351/365 * 350/365 * 349/365 * 348/365 * 347/365 * 346/365 * 345/365 * 344/365 * 343/365 * 342/365 * 341/365 * 340/365 * 339/365 * 338/365 * 337/365 * 336/365

So the probability of 2 people *not* having a common birthday out of 30 people is 0.293683757.

To get the probability of 2 people having a common birthday, you simply need to subtract our result from 1:

1 - 0.293683757 = 0.706316243

So in a room of 30 people, you have a 70.6% chance of finding 2 people with the same birthday.

Q.E.D.

You can read about the problem here: http://en.wikipedia.org/wiki/Birthday_problem