[" The number of permutations of "8" things "],[" taken 'r' at a time is "1680." Then "r=]

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

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

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

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

The number of circular permutations of 7 dissimilar things taken 5 at a time is

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

The no.of all permutation of n distinct things taken all at a time is n!

Find the number of permutations of 8 things, taken 3 at a time, in which 2 particular things are always : included .

Find the number of permutations of 8 things, taken 3 at a time, in which 2 particular things are always : excluded .

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.