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14.Probability
easy
A bag contains $4$ white, $5$ red and $6$ black balls. If two balls are drawn at random, then the probability that one of them is white is
A
$\frac{{44}}{{105}}$
B
$\frac{{11}}{{105}}$
C
$\frac{{11}}{{21}}$
D
None of these
Solution
(a) Required probability $=P(WR) + P(WB) $$= \frac{{^4{C_1}{(^5}{C_1}{ + ^6}{C_1})}}{{^{15}{C_2}}}$
$ = \frac{{{}^4{C_1}\,.\,11}}{{{}^{15}{C_2}}} = \frac{{4\,.\,11\,.\,2}}{{15\,.\,14}} = \frac{{44}}{{105}}.$
Standard 11
Mathematics