What is the probability of getting exactly 3 tails when four coins are tossed?

Question

what is the probabilty of getting exactly 3 tails when 4 coins are tossed?

Answer 1

P(exactly 3 tails on 4 coins) = P(3 tails on 3 coins) * P(1 tail on 1 coin) * (# of ways to arrange 3 t's and 1 h)

P(exactly 3 tails on 4 coins) = 1/8 * 1/2 * 4

P(exactly 3 tails on 4 coins) = 1/4

 

All combos:  hhhh, hhht, hhth, hhtt, hthh, htht, htth, httt thhh, thht, thth, thtt, tthh, ttht, ttth, tttt

Want these:  httt, thtt, ttht, ttth

Result:  4 / 16 = 1/4