$\sum \limits_{ k =0}^6{ }^{51- k } C _3$ is equal to
${ }^{51} C _4-{ }^{45} C _4$
${ }^{51} C _3-{ }^{45} C _3$
${ }^{52} C _4-{ }^{45} C _4$
${ }^{52} C _3-{ }^{45} C _3$
There are $m$ books in black cover and $n$ books in blue cover, and all books are different. The number of ways these $(m+n)$ books can be arranged on a shelf so that all the books in black cover are put side by side is
In the $13$ cricket players $4$ are bowlers, then how many ways can form a cricket team of $11$ players in which at least $2$ bowlers included
The number of words (with or without meaning) that can be formed from all the letters of the word $"LETTER"$ in which vowels never come together is
A person is permitted to select at least one and at most $n$ coins from a collection of $(2n + 1)$ distinct coins. If the total number of ways in which he can select coins is $255$, then $n$ equals
It is required to seat $5$ men and $4$ women in a row so that the women occupy the even places. How many such arrangements are possible?