Hi Binomial Distribution: p = 1/2 and q = 1/2 n = 4 (coins) Using Calculator (TI instructions given here) An inexpensive, easy to use Casio fx-115 ES plus works similarly P(At least 3 head)= P(x ≥ 3) = 1- P(x ≤ 2) 1 - binomcdf(4,.5,2) = 1 - .6875 = .3125 0r 31.25% P(At most 2 head) = P(x ≤ 2) = binomcdf(4,.5,2) =.6875 0r 68.75% P(Exactly 1 head) = P(x=1) = binompdf(4,.5,1) = .25 0r 25% One would expect, over the 15 times of tossing the 4 coins.. on an average... the above percentages would hold true. Wish You the Best in your Studies.