Total number of words formed by 2 vowels and 3 consonants taken from 4 vowels and 5 consonants is equal to

The number of different four digit numbers that can be formed with the digits 2, 3, 4, 7 and using each digit only once is

The sum of the digits in unit place of all the numbers formed with the help of 3, 4, 5 and 6 taken all at a time is

A five digit number divisible by 3 is to be formed using the numbers 0, 1, 2, 3, 4 and 5 without repetitions. The total number of ways this can be done is

Everybody in a room shakes hands with everybody else. The total number of hand shakes is 66. The total number of persons in the room is