How many $3$-letter words can be formed from the letters of the word '$EXPERTISE$',if repetition of letters is not allowed?

The sum of all three-digit numbers,formed using non-zero digits,where all the digits are perfect squares of a natural number,is:

In how many ways can $15$ different books be divided equally among $3$ sets or groups?

$A$ man has $10$ friends. In how many ways can he invite one or more of them to a party?

$A$ dictionary is printed consisting of $7$-letter words only that can be formed using the letters of the word $CRICKET$. If the words are arranged in alphabetical order,as in an ordinary dictionary,then the number of words before the word $CRICKET$ is:

The total number of $3$-digit numbers,whose sum of digits is $10$,is