The greatest positive integer which divides $(n+16)(n+17)(n+18)(n+19)$,for all positive integers $n$,is

The number of ways in which one or more balls can be selected out of $10$ white,$9$ green,and $7$ blue balls is:

There are $6$ different novels and $3$ different poetry books on a table. If $4$ novels and $1$ poetry book are to be selected and arranged in a row on a shelf such that the poetry book is always in the middle,then the number of such possible arrangements is

In a football championship,there were played $153$ matches. Every team played one match with each other. The number of teams participating in the championship is

All possible two-factor products are formed from the numbers $1, 2, 3, 4, \dots, 200$. The number of products out of the total obtained which are multiples of $5$ is:

$A$ set contains $(2n + 1)$ elements. The number of subsets of the set which contain at most $n$ elements is: