A bag contains 10 white balls and 15 black balls. Two balls drawn in succession. The probability that one of them is black the other is white is

Let A be the set of all nonsingular matrices over real numbers and let * be the matrix multiplication operator. Then

The number of elements in the power set $$P(S)$$ of the set $$S = \left\{ {\left\{ \phi \right\},1,\left\{ {2,3} \right\}} \right\}$$ is

Let $$R$$ be a symmetric and transitive relation on a set $$A$$. Then