How many permutations of 3 different digits are there, chosen from the ten digits 0 to 5 inclusive?

The number of ways in which three boys can be seated on five chairs?

A special type of password consists of four different letters of the alphabet, where each letter is used only once. How many different possible passwords are there?

Complete:

The number of times the digit 3 will be written when listing the integers from 1 to 1000 is ___________.

How many 3 letter words with or without meaning can be formed out of the letters of the word SMOKE when repetition of words is allowed?

How many permutations of 4 different letters are there, chosen from the twenty six letters of the alphabet?

 How many permutations of 3 different letters are there, chosen from the four letters of the alphabet?

Complete:

The exponent of 3 in 100 !, is _________.

 How many permutations of 3 different digits are there, chosen from the ten digits 0 to 9 inclusive?

If the permutation of  a,b,c,d,e taken all together be written down in alphabetical order as in dictionary and numbered, then the rank of the permutation debac is: