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If  R=P(phi) and T=P({1,2}) where P is power set

Then cardinality for S=R * T is ?


What i know is phi *{Any set} = phi  so above cardinality must be zero too.

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power set of empty set = $p(\phi )=\left \{ \Phi \right \}  , powerset of singleton set=p(\left \{ \phi \right \})= \left \{ \phi ,\left \{ \phi \right \} \right \}$

as we know if a set contain n element then power set will contain $2^{n}$

so here empty set contain 0 element so p(empty set) contain $2^{0}=1$

and singleton set has 1 element so power set will contain $2^{1}=2$

so for given question |R|=1 and |T|=4 , S= 1*4=4 ans .
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