How many different ways can the letters in the word $ATTEND$ be arranged?

The number of ways in which five identical balls can be distributed among ten identical boxes such that no box contains more than one ball,is

There are $n$ white and $n$ black balls marked $1, 2, 3, ..., n$. The number of ways in which we can arrange these balls in a row so that neighbouring balls are of different colours are

If $n$ is even and the value of $^nC_r$ is maximum,then $r = $

The number of numbers that can be formed with the help of the digits $1, 2, 3, 4, 3, 2, 1$ so that odd digits always occupy odd places,is

In how many ways can $10$ people line up at a ticket window of a cinema hall?