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QUESTION

If $p(A)=0.3,\ p(B)=0.8$ and $p(A$ or $B)=0.9$, what is $p(A$ and
$B)?$

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ANSWER

$p(A$ or $B)=p(A)+p(B)-p(A$ and $B)$,

therefore $p(A$ and $B)=p(A)+P(B)-p(A$ or $B)=0.3+0.8-0.9=0.2$




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