hi I was wondering if anyone could help me figure this question out I think it is binomial distibution but I'm honestly not sure
If 20 coins are dropped on a table. what is the probability ( to three decimal places ) that
a) exactly 12 coins are heads
b) At least 12 coins are heads
if anyone could help me that would be great!
November 2nd 2008, 09:31 PM
It is in fact the binomial distribution because the trials are independent of each other and you are counting the number of successes with a given number of trials.
Let X be the number of heads.
P(X=12) = (20 C 12)*(0.5^12)*(0.5^8)
I'll let you do the computation yourself.
Note from (a), the binomial distribution will always be a comination multiplied by 0.5^20
P(X>=12) = P(X=12)+P(X=13)+P(X=14)+...+P(X=20)
For each probability, just sub in the X value (eg. P(X=13) = (20 C X)*(0.5^20)