Question

An unbiased coin is tossed 4 times find the chance that the tail will appear exactly 3 times

Answer 1

Total no. of possibilities/outcomes: (2^4) = 16

Number of times tail appears exactly 3 times is:
C(4,3) = 4

Now, the probability that tail appears exactly 3 times = 4/16 = 1/4

This is one method. There is another method where u write down the sample space and check the probability. But that method is tedious. So i recommend the above method.