In how many ways 4 persons can occupy 10 chairs in a row, if no two sit on adjacent chairs?

In how many ways can 5 people occupy 8 vacant chairs?

In how many ways 12 boys can be seated on 10 chairs in a row so that two particular boys always take seat?

In how many ways can 10 boys and 10 girls sit in a row so that no two boys sit together ?

In how many ways 6 girls can be seated in two chairs ?

In how many ways 5 persons can sit at a round table,if two of the persons do not sit together?

In how many ways can 2 boys and 3 girls sit in a row so that no two girls sit side by side?

In how many ways 4 boys and 3 girls be seated in a row of 7 chairs if the boys and girls are to be seated alternately and the boys occupy odd places.