Find the number of permutations of n different things taken r at a time such that two specific things occur together?

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

If the number of permutations of n different things taken 4 at a time in which one particular thing does not occur is equal to that in which it does occur,find n .

Find the number of permutations of 10 objects, taken 4 at a time.

Find the number of permutations of 7 objects, taken 3 at a time.

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

Prove that the no.of permutations of n different objects taken r at a time in which two specified objects always occur together 2!(r-1)(n-2)P_(r-2)

Find the number of permutations of n distinct things taken r together, in which 3 particular things must occur together.