A coin is biased so that the head is 3 times as likely to occur

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968. A coin is biased so that the head is 3 times as likely to occur as tail. If the coin is tossed twice, find the probability distribution of number of tails.


Let p be the probability of obtaining a head when a coin is tossed once and q that of obtaining a tail
From given condition,
                p = 3 q,       p + q = 1
therefore space space space space space 3 space straight q space plus space straight q space equals space 1 space space space space space space space space space space space space space space space rightwards double arrow space space space space 4 space straight q space equals space 1 space space space space space rightwards double arrow space space space space straight q space equals space 1 fourth
therefore space space space space straight p space equals space 3 space straight q space equals space 3 over 4.
Let X denote the number of tails in two tosses of the coin, then X can take values 0, 1 and 2.
                            straight P left parenthesis straight X space equals 0 right parenthesis space equals space space straight P left parenthesis no space tail right parenthesis space equals space straight P left parenthesis HH right parenthesis space equals space straight p space straight p space space equals space 3 over 4 cross times 3 over 4 space equals 9 over 16
straight P left parenthesis straight X space equals space 1 right parenthesis space equals space straight P left parenthesis one space tail space and space one space head right parenthesis
space space space space space space space space space space space space space space space space space equals space straight P left parenthesis HT comma space TH right parenthesis space equals space straight P left parenthesis HT right parenthesis space plus space straight P left parenthesis TH right parenthesis
space space space space space space space space space space space space space space space space space equals space straight p space straight q space plus space straight q space straight p space space equals space 2 space straight p space straight q space equals space 2 cross times 3 over 4 cross times 1 fourth space equals 6 over 16

and          straight P left parenthesis straight X space equals space 2 right parenthesis space equals space straight P left parenthesis two space tails right parenthesis space equals space straight P left parenthesis TT right parenthesis space equals space qq space equals 1 fourth cross times 1 fourth space equals 1 over 16
∴   probability distribution of X is

      

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