How many numbers of four digits can be formed with the digits $1, 2, 3, 4$ and $5$?

There are four balls of different colours and four boxes of colours same as those of the balls. The number of ways in which the balls,one in each box,could be placed such that a ball does not go to the box of its own colour is

There are $16$ points in a plane, out of which $6$ are collinear. How many lines can be drawn by joining these points?

$5$-digit numbers are to be formed using $2, 3, 5, 7, 9$ without repeating the digits. If $p$ is the number of such numbers that exceed $20000$ and $q$ is the number of those that lie between $30000$ and $90000$,then $p : q$ is

How many words (with or without meaning) of $3$ distinct English alphabets can be formed?

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