Comment by werdnapk

The example for even numbers should be:

even_numbers = [1, 2, 3, 4, 5].find_all { |element| element.even? }

or

even_numbers = [1, 2, 3, 4, 5].find_all(&:even?)

instead of:

even_numbers = [1, 2, 3, 4, 5].map { |element| element if element.even? }