If $$a_1, a_2, a_3, \ldots, a_{10}$$ is a geometric progression and $$\frac{a_3}{a_1}=25$$, then $$\frac{a_9}{a_5}$$ equals

If the set $$x$$ contains 7 elements and set $$y$$ contains 8 elements, then the number of bijections from $$x$$ to $$y$$ is

If the middle term of the AP is 300, then the sum of its first 51 terms is

If the sum of $$n$$ terms of an AP is given by $$S_n=n^2+n$$, then the common difference of the $$\mathrm{AP}$$ is