The number of words that can be formed with the letters of the word 'DEFINITE' if two vowels are together and the other two are also together but separated from the first two is

How many natural numbers are there between 100 and 1000 such that at least one of their digits is $6 ?$

If ${ }^{n+2} C_8:{ }^{n-2} P_4=57: 16$, then ' $n$ ' is

On each working day of a school there are six periods. The number of ways in which five subjects are arranged if each subject is allotted at least one period and no period remains vacant is