A math question

[Annie~]

A fair coin is tossed 6 times. what is the probability that exactly 2 heads will show?
The answer is 15/64.

Does anyone know where they get 64 from?

[isd121]

P(2 heads) = C(6,2) (1/2)^2 (1/2)^4 = 15/64
This is an example of binomial probability. For explanation check this website
http://mathforum.org/library/drmath/view/56189.html

Originally Posted by Annie~

A fair coin is tossed 6 times. what is the probability that exactly 2 heads will show?
The answer is 15/64.

Does anyone know where they get 64 from?

[sgdorfl90]

Originally Posted by Annie~

A fair coin is tossed 6 times. what is the probability that exactly 2 heads will show?
The answer is 15/64.

Does anyone know where they get 64 from?

ok...a very simple way of doing it...there are 6 ways of getting the first head....it could be in any 6 tosses, and then once u have 1 head...there are 5 ways of getting second head, cuz one has been taken care of. But within it, order doesn't matter...so we do 6*5/2=15. Now, there is 1/2 of getting 1 head, and same for second, but we have to account for 4 tails which has equal prob. So, its (1/2)^6= 1/64*15 ways= 15/64

[Annie~]

Thanx for the help.

[fob12]

Originally Posted by mybaa

ok...a very simple way of doing it...there are 6 ways of getting the first head....it could be in any 6 tosses, and then once u have 1 head...there are 5 ways of getting second head, cuz one has been taken care of. But within it, order doesn't matter...so we do 6*5/2=15. Now, there is 1/2 of getting 1 head, and same for second, but we have to account for 4 tails which has equal prob. So, its (1/2)^6= 1/64*15 ways= 15/64

matter...so we do 6*5/2=15.

Does anyone know why do you divide 6*5 by 2?