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14.Probability
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Three athlete $A, B$ and $C$ participate in a race competetion. The probability of winning $A$ and $B$ is twice of winning $C$. Then the probability that the race win by $A$ or $B$, is
A
$\frac{2}{3}$
B
$\frac{1}{2}$
C
$\frac{4}{5}$
D
$\frac{1}{3}$
Solution
(c) $P(A) = P(B) = 2P(C),$
$P(A) + P(B) + P(C) = 1$
$ \Rightarrow P(C) = \frac{1}{5}$and $P(A) = P(B) = \frac{2}{5}$
Hence $P(A \cup B) = P(A) + P(B) = \frac{2}{5} + \frac{2}{5} = \frac{4}{5}.$
Standard 11
Mathematics
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