Find the number of permutations of 20 things taken 5 at a time so that one particular thing will never occur.

Find the number of permutations of 20 things taken 5 at a time so that one particular thing will always occur

Find the number of permutations of n things, taken r at a time, in which 3 particular things : will never occur.

Find the number of permutations of n things taken r at a time in which two particular things : never occur.

Find the number of permutations of n different things taken r at time so that m(ltr) particular things will never occur.

Find the number of permutations of n things taken r at a time in which two particular things : (i) always occur (ii) never occur.

Find the number of permutations of n things, taken r at a time, in which 3 particular things : (i) always occur (ii) will never occur.

Find the number of permutations of n things taken r at a time in which two particular things : always occur.

Find the number of permutations of n things, taken r at a time, in which 3 particular things : always occur.

2.The number of permutations of 8 things taken at a time is 1680, Then r=

The number of circular permutations of 8 things taken 4 at a time is