
data managment help!
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!

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.
For (a),
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.
For (b),
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)
Once again, I'll leave the computation up to you.