Question

how to calculate 13C2

Answer 1

Answer:

13C2 = 78

Step-by-step explanation:

Formula

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

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:

$13C2=\dfrac{13!}{2!(13-2)!}$

        $=\dfrac{13!}{2! \ 11!}$

        $=\dfrac{13 \times 12 \times 11 \times 10 \times 9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1 }{2 \times 1 \times 11 \times 10 \times 9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1}$

        $=\dfrac{13 \times 12}{2 \times 1}$

        $=\dfrac{156}{2}$

        $=78$