How many words can be made from the letters of the word $DELHI$,if $L$ comes in the middle in every word?

$\sum_{0 \le i < j \le n} i \binom{n}{j}$ is equal to

There are $n$ points in a plane of which $p$ points are collinear. How many lines can be formed from these points?

Given $6$ different letters of an alphabet. Words with $4$ letters are formed from these given letters. The number of words which have at least one letter repeated and no two same letters are together,is:

In an election there are $8$ candidates,out of which $5$ are to be chosen. If a voter may vote for any number of candidates but not greater than the number to be chosen,then in how many ways can a voter vote?

How many numbers lying between $500$ and $600$ can be formed with the help of the digits $1, 2, 3, 4, 5, 6$ when the digits are not to be repeated?