Blocks

There are 9 interactive basic building blocks of an organization. How many two-blocks combinations are there?

Result

n =  36

Solution:

$C_{{ 2}}(9) = \dbinom{ 9}{ 2} = \dfrac{ 9! }{ 2!(9-2)!} = \dfrac{ 9 \cdot 8 } { 2 \cdot 1 } = 36 \ \\ \ \\ n = { { 9 } \choose 2 } = 36$

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