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14.Probability
medium
A drawer contains $5$ brown socks and $4$ blue socks well mixed. A man reaches the drawer and pulls out $2$ socks at random. What is the probability that they match
A
$\frac{4}{9}$
B
$\frac{5}{8}$
C
$\frac{5}{9}$
D
$\frac{7}{{12}}$
Solution
(a) Out of $9$ socks, $2$ can be drawn in ${}^9{C_2}$ ways.
Two socks drawn from the drawer will match if either both are brown of both are blue.
Therefore favourable number of cases is ${}^5{C_2} + {}^4{C_2}.$
Hence the required probability $ = \frac{{{}^5{C_2} + {}^4{C_2}}}{{{}^9{C_2}}} = \frac{4}{9}.$
Standard 11
Mathematics