20!/(18!*2!) * (1/2)^20 = 190/1048576 = 0.000181198...
So less than 1 in 5000.
The probability of flipping a quarter and getting heads is 1 in 2. the probability of rolling a die and getting 6 is 1 in 6.
The probability of flipping a coin 3 times and getting 3 heads is 1/2
The probability is 0.375
The probability of this is 50%. 2/4
There are 8 permutations of flipping a coin 3 times, or of flipping 3 coins one time. They are, with the permutations of two heads bolded...TTTTTHTHTTHHHTTHTHHHTHHH... thus, the probability of flipping a coin 3 times and getting 2 heads is 3 in 8, or 0.375.
The probabilty of you flipping 3 coins and getting all heads or tails is 0.125 or 1/8.
The probability of NOT getting heads is (1/2)4=1/16 Therefore the probability of getting heads is 1-1/16=15/16
The probability is 25%. The probability of flipping a coin once and getting heads is 50%. In your example, you get heads twice -- over the course of 2 flips. So there are two 50% probabilities that you need to combine to get the probability for getting two heads in two flips. So turn 50% into a decimal --> 0.5 Multiply the two 50% probabilities together --> 0.5 x 0.5 = 0.25. Therefore, 0.25 or 25% is the probability of flipping a coin twice and getting heads both times.
.125
1/4
i got 1/941192
0.54 or 0.0625 or 1/16.