N Choose K Formula

N choose K is called so because there are (n/k) number of ways to choose k elements, irrespective of their order from a set of n elements.

To calculate the number of happening of an event, N choose K tool is used. N is the sum of data and K is the number that we chose from the sum of data.

The formula for N choose K formula is :

\(_{n}^{k}\textrm{C}= \frac{n!}{k!(n-k)!}\)

n is the total number
k is the number of selected item

Solved Examples

Question 1: How many ways to draw exactly 6 cards from a pack of 10 cards?


From the question it is clear that,
n = 10
k = 6

So the formula for n choose k is,

\(_{n}^{k}\textrm{C}=\frac{n!}{k!(n-k)!}\) \(_{10}^{6}\textrm{C}=\frac{10!}{6!(10-6)!} =\frac{3628800}{17280}\)

= 210

So, there are 210 ways of drawing 6 cards in a pack of 10.

Practise This Question

Which of the following statements is correct regarding friction between two surfaces in contact?