6 coins are tossed. what is the probability of getting 4 tails?

Question

thanks :) I'm stuck on using (nCr)*(P^r)*(q^n-r) 

Answer 1

p = ½ (probability of success, tail) so q also = ½.

 

This is a binomial distribution (Bernoulli trials) with n = 6; the # of ways that 4 tails may occur in 6 flips of coin is 6C4 = 15.

 

The individual term of the binomial expansion corresponding to 4 successes & 2 failures is ₆C₄•(½)⁴•(½)² = 15/2⁶ = 0.234375

Answer 2

Maybe this will help.... http://math.stackexchange.com/questions/800997/flip-a-coin-6-times-what-is-probability-of-at-least-4-heads