Question

How to calculate 13C2

Answer 1

13C2 = 78

Explanation:

Formula

`nCr=(n!)/(r!(n-r)!)`

The ! symbol in math is called "factorial". When placed after a number, it means to multiply the number by every natural number below it.

For 13C2:

• n = 13
• r = 2

Substitute these values into the formula:

`13C2=(13!)/(2!(13-2)!)`

`=(13!)/(2! \ 11!)`

`=(13 * 12 * 11 * 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1 )/(2 * 1 * 11 * 10 * 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1)`

`=(13 * 12)/(2 * 1)`

`=(156)/(2)`

`=78`