The total number of selections of atleast one thing at most r things from `(2r + 1)` different things is 255. Then the value of r is

Number of ways of selecting r consecutive things out of n things

If the ratio of the total number of combinations of 2n different things to the total number of combinations of n different things is 1025:1 find n.

If the ratio of the total number of combinations of 2n different things to the total number of combinations of n different things be 1025 : 1 , find n .

The number of ways of selecting one or more things out of n dissimilar things is

Find the number of selections of one or more things from the group of p identical things of one type, q identical things of another type, r identical things of the third type and n different things.

Find the number of selections of one or more things from the group of p identical things of one type, q identical things of another type, r identical things of the third type and n different things.

Show that the total number of permutations of n different things taken not more than r at a time, when each thing may be repated any number of times is (n(n^(r)-1))/((n-1)) .