Permutations & Combinations :Revision

Find the number of ways in which 5 boys and 5 girls be seated in a row so that no two girls may sit together. 

How many words each of 3 vowels and 2 consonants can be formed from the letters of the word INVOLUTE?

In an examination a candidate has to pass in each of the four subjects. In how many ways can he fail?

If , find n.