How namy subsets with $3$ elements of set $S=\{1,2,3,...,19,20\}$ exist, such that their product is divisible by $4$.
Problem
Source: Regional Olympiad - Federation of Bosnia and Herzegovina 2014
Tags: combinatorics, Divisibility
Source: Regional Olympiad - Federation of Bosnia and Herzegovina 2014
Tags: combinatorics, Divisibility
How namy subsets with $3$ elements of set $S=\{1,2,3,...,19,20\}$ exist, such that their product is divisible by $4$.