Khan/khan-exercises — Issue #12564: Probability 1 - A fair coin is flipped four times. What is the probability of getting tails at least twice?
Author: KhanBugz
Created: 2012-01-31 16:52:08+00:00
State: open
Labels: firefox, hard, win7

Reporter: fantasycomedian@gmail.com

The Khan Academy Answer said: 11/16

I would like a full explanation of how it came to that conclusion. Is there a way to find the answer out by mathematical means rather than doing by long "diagram" means...

[probability_1.html?seed=142&problem=2](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/probability_1.html?seed=142&problem=2&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/probability_1.html?seed=142&problem=2&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5C%227%2F8%5C%22%22%2C26%5D%2C%5B%22incorrect-activity%22%2C%22%5C%221%2F4%5C%22%22%2C6%5D%2C%5B%22hint-activity%22%2C%220%22%2C43%5D%2C%5B%22hint-activity%22%2C%220%22%2C43%5D%2C%5B%22hint-activity%22%2C%220%22%2C44%5D%2C%5B%22hint-activity%22%2C%220%22%2C44%5D%5D)

["7/8","1/4"]

Mozilla/5.0 (Windows NT 6.1; WOW64; rv:9.0.1) Gecko/20100101 Firefox/9.0.1

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