There are 4 possible outcomes, HH, HT, TH, TT. If we assume the odds of tossing heads or tails on any toss is 1/2 (50:50) the odds of tossing heads twice in a row is 1/4 (or 25%).
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the only combination which does not produce heads at least once it tails twice. the odds of getting tails twice is 0.5*0.5=0.25 so the odds for getting heads at least once is 1-0.25=0.75 or 75% or 3/4.
"The same as getting heads the first time, a one-in-two chance." No It's Not! "One in two chance" means 50/50 chance. The odds of getting 2 in a row are not 50/50. I don't know what it is because that's how I arrived at this question. But if my friend were to bet me that he could get to heads in a row.... I'd take him up on that bet everytime, saying that he couldn't. He'd win a couple times here and there but in the end would lose money. It's not 50/50.
There is a fifty percent chance of the coin landing on "heads" each time it is flipped.However, flipping a coin 20 times virtually guarantees that it will land on "heads" at least once in that twenty times. (99.9999046325684 percent chance)You can see this by considering two coin flips. Here are the possibilities:Heads, heads.Heads, tails.Tails, tails.Tails, heads.You will note in the tossing of the coin twice that while each flip is fifty/fifty, that for the two flip series, there are three ways that it has heads come up at least once, and only one way in which heads does not come up.In other words, while it is a fifty percent chance for heads each time, it is a seventy five percent chance of seeing it be heads once if you are flipping twice.If you wish to know the odds of it not being heads in a twenty time flip, you would multiply .5 times .5 times .5...twenty times total. Or .5 to the twentieth power.That works out to a 99.9999046325684 percent chance of it coming up heads at least once in the twenty times of it being flipped.
The probability is 0.0198. The probability of that happening twice is 0.000393 Is this the odds of it happening twice with the same number?
The odds of rolling a 7 are 1/6. The odds of rolling two in a row are 1/36. The odds of rolling an 11 are 1/18. The odds of rolling two in a row are 1/324. The odds of rolling doubles are 1/6. The odds of rolling double twice in a row are 1/36.