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

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