Basic statistics [duplicate]

I was wondering, if you flip a coin 100 times, what is the chance of getting 10 heads or 10 tails in a row? I think this could be a good way to respond to people who think that unlikely things don't happen by chance ( I suspect the chances are over 50%), but I don't know how to do the math.

marked as duplicate by J. M. is a poor mathematician, joriki, Mike Spivey, Asaf Karagila♦, Hans LundmarkAug 18 '11 at 20:50

• When people invent a sequence of data, that fact can often be detected from the paucity of runs. Also, if the data are to one decimal place, there will be a paucity of numbers ending in $.0$ and (to a lesser degree) $.5$. But a true scientist would never never invent data. Never. Or at least would be smart enough to use a random number generator. – André Nicolas Aug 18 '11 at 19:24