The ratio of successful events A = 4 to total number of possible combinations of sample space S = 8 is the probability of 2 tails in 3 coin tosses.
4/8 = 0.5
Possible outcomes of tossing three coins are:
(HHH), (HHT), (HTH), (THH), (TTT), (TTH), (THT),(HTT)
here H and T are denoted for Head and Tail.
Total outcomes = 8
no. of outcomes with at least two tailsG = 4