N r For n r 0. N stands for the number of items and r stands for the number of items we have to. Combinations gives the number of ways a subset of r items can be chosen out of a set of n items.
Arranging people digits numbers alphabets letters and colours are examples of permutations.
It has been stated below. The nCr formula is. N - r where n represents the number of items and r represents the number of items being chosen at a time. Use that fact to derive a summation formula involving expressions nC1 Im not entirely sure what this means but Im assuming we are to use Sigma.