In how many ways can 21 English and 19 Hindi books be placed in a row so that no two hindi books are together?

In how many ways can 4 Indians and 4 Pakistanis is to be seated at around table so that no two Indians may be together?

In how many ways can 5 boys and 5 girls be seated around a table so that no two boys are adjecent?

In how many ways can 5 keys be put in a ring?

In how many ways can 6 boys and 6 girls sit in a round table so that no two boys sit together

In how many ways can 5 boys and 5 girls sit in a circle so that no two boys sit together?

In how many ways 4 boys and 3 girls can be seated in a row so that they are alternate.

In how many ways can 8 Indians and, 4 American and 4 Englishmen can be seated in a row so that all person of the same nationality sit together?