When a coin is tossed 4 times. A total of 24 = 16 outcomes are possible.
Let S be the set consisting of all such outcomes.
∴ n(S) = 16
Let A be the event of getting 2 tails.
∴ A = {TTHH,THTH,THHT,HTTH,HTHT,HHTT}
∴ n(A) = 6
∴ P(A) = \(\frac{6}{16} \)= \(\frac{3}{8}\)
Let B be the event of getting 3 tails.
∴ B = { TTTH ,TTHT, THTT,HTTT }
⇒ n(B) = 4
∴ P(B) = \(\frac{4}{16}\)= \(\frac{1}{4}\)
We need to find the probability of getting 2 tails or 3 tails i.e.
P(A∪B) = ?
As we can’t get 2 and 3 tails at the same time. So A and B are mutually exclusive events.
∴ P(A∪B) = P(A) + P(B) = \(\frac{3}{8}\) + \(\frac{1}{4}\)= \(\frac{5}{8}\)