Weekly service

In the class are 20 pupils. How many opportunities have the teacher if he wants choose two pupils randomly who will weeklies?

Result

n =  190

Solution:

n=C2(20)=(202)=20!2!(20−2)!=20⋅192⋅1=190n = C_{{ 2}}(20) = \dbinom{ 20}{ 2} = \dfrac{ 20! }{ 2!(20-2)!} = \dfrac{ 20 \cdot 19 } { 2 \cdot 1 } = 190

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