$^nC_r \div ^nC_{r-1} = $

Out of $13$ cricket players,$4$ are bowlers. In how many ways can a team of $11$ players be selected such that the team contains at least $2$ bowlers?

$A$ committee of $4$ persons is to be formed from $2$ ladies,$2$ old men,and $4$ young men such that it includes at least $1$ lady,at least $1$ old man,and at most $2$ young men. The total number of ways in which this committee can be formed is:

$A$ man has $10$ friends. In how many ways can he invite one or more of them to a party?

In how many ways can $35$ apples be distributed among $3$ boys such that each boy can have any number of apples?

$^{20}C_1 + 3 ^{20}C_2 + 3 ^{20}C_3 + ^{20}C_4$ is equal to-