The formula for nCr, also known as the binomial coefficient, is used to determine the number of ways to choose r elements from a set of n elements without regard to the order. It is given by the formula:

$nCr = \binom{n}{r} = \frac{n!}{r!(n - r)!}$

Where:

• n! (n factorial) is the product of all positive integers up to n.
• r! (r factorial) is the product of all positive integers up to r.
• (n - r)! is the factorial of (n - r).

For example, if you want to calculate 5C2 (choosing 2 items from 5), the calculation would be:

[ \binom{5}{2} = \frac{5!