Question

20 coins are flipped. What is the probability of getting 15 or more heads?

Please show the work and simplify the formula.

Answer 1

Solution:

Here , n = number of coins = 20

k = Number of getting heads = 15

p = Probability of head for single coin = 0.5

We have to find P( x 15 ) = _____?

That is 1 - P( x 14 ) = _________?

Using excel formula ..........  =1-BINOMDIST(14,20,0.5,TRUE)

P( x 15 ) = 0.0207

If you want to use binomial formula then you can use it,

where   

Just repeat the procedure by putting n = 20,p=0.5 and q = 0.5 for each k = 15,16,17,18,19 and 20

And add all these probabilities.

You will get final probability as 0.0207

Done