n above k that is n choose k that is binomial coefficient
Proof of the Binomial Distribution Factorial Formula - YouTube
How To Use nCr On A Calculator | Factorial Function x! Casio fx-83GT fx-85GT fx-300ES - YouTube
ELI5: In probability, how does the binomial coefficient (n choose k) calculate the possible number of ways you can have k successes in n trials? : r/explainlikeimfive