From a group of persons the number of ways of selecting 5 persons is equal to that of 8 persons.No. of ways of selecting 2 persons is

The number of ways of dividing 20 persons into 10 couples is

The number of ways of dividing 20 persons into 10 couples is

The number of ways of arranging 7 persons around a circle is

10 persons are seated at round table then the number of ways of selecting 3 persons out of them if no two persons are adjacent to each other is

The number of ways can 9 things be divided equally among 3 persons is

Ten persons are arranged in a row.The number of ways of selecting four persons so that no two persons sitting next to each other are selected is