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14.Probability
hard
Let $X$ be a set containing $10$ elements and $P(X)$ be its power set. If $A$ and $B$ are picked up at random from $P(X),$ with replacement, then the probability that $A$ and $B$ have equal number elements, is
A
$\frac{{\left( {{2^{10}} - 1} \right)}}{{{2^{10}}}}$
B
$\frac{{^{20}{C_{10}}}}{{{2^{10}}}}$
C
$\frac{{\left( {{2^{10}} - 1} \right)}}{{{2^{20}}}}$
D
$\frac{{^{20}{C_{10}}}}{{{2^{20}}}}$
(JEE MAIN-2015)
Solution
Required porbability is
$\frac{{{{\left( {^{10}{C_0}} \right)}^2} + {{\left( {^{10}{C_1}} \right)}^2} + {{\left( {^{10}{C_2}} \right)}^2} + …… + {{\left( {^{10}{C_{10}}} \right)}^2}}}{{{2^{10}}}}$
$ = \frac{{{\,^{20}}{C_{10}}}}{{{2^{20}}}}$
Standard 11
Mathematics