If $$A=\{x \mid x \in N, x \leq 5\},B=\left\{x \mid x \in Z, x^2-5 x+6=0\right\}$$, then the number of onto functions from $$A$$ to $$B$$ is

On the set of positive rational, a binary operation * is defined by $$a * b=\frac{2 a b}{5}$$. If $$2 * x=3^{-1}$$, then $$x=$$

If $$U$$ is the universal set with 100 elements; $$A$$ and $$B$$ are two set such that $$n(A)=50, n(B)=60, n(A \cap B)=20$$ then $$n\left(A^{\prime} \cap B^{\prime}\right)=$$