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Consider the experiment oftossing a coin. If the coin shows head, toss it again but if it shows tailthen throw a die. Find the conditional probability of the event that the dieshows a number greater than 4 given that there is at least one tail |
Answer» According to the equation, sample space `S = {(H,H),(H,T),(T,1),(T,2),(T,3),(T,4),(T,5),(T,6)}` In the above set, there are 8 elementary events, but all are not equally likely. However, events (H,H) and (H,T) are equally likely. Each event has probability `(1)/(4)` (considering sample space `{HH, HT, TH, T T}` Events (T, 1), (T, 2), ...,(T, 6) are also equally likely. Let probability of each be p. Then `6p = 1 - (1)/(4) - (1)/(4) = (1)/(2)` `therefore p = (1)/(12)` Let event A be 'the dice shows a number greater than 4', and event B be 'there is at least one tail'. `therefore A = {(T, 5),(T, 6)}` `"and "B = {(H,T),(T,1),(T,2),(T,3),(T,4),(T,5),(T,6)}` `therefore P(A) = (1)/(12) + (1)/(12) = (1)/(6)` `P(B) = (1)/(4) + (1)/(12) + (1)/(12) + (1)/(12) + (1)/(12) + (1)/(12) + (1)/(12)=(1)/(4) + (1)/(2) = (3)/(4)` |
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