array.find(1..10).detect { |i| i % 5 == 0 and i % 7 == 0 } #=> nil (1..10).find { |i| i % 5 == 0 and i % 7 == 0 } #=> nil (1..100).detect { |i| i % 5 == 0 and i % 7 == 0 } #=> 35 (1..100).find { |i| i % 5 == 0 and i % 7 == 0 } #=> 35You can just use a set difference (aka minus) to see if one array includes all elements of another not_included = [1,2,3] - (1..9).to_a not_included # => [] not_included = [1,2,3,'A'] - (1..9).to_a not_included # => ["A"]