I'd recommend going through the methods of Enumerable (see http://ruby-doc.org/core-2.3.1/Enumerable.html) and practicing usage of each one so you can get familiar with them - most of these methods are very useful in the real world and for code kata!

It shouldn't!

[1] pry(main)> def test_even(n)
[1] pry(main)*   n % 2 == 0
[1] pry(main)* end
=> :test_even
[2] pry(main)> test_even(2.0)
=> true
[3] pry(main)> 2.0 % 2
=> 0.0
[4] pry(main)> 0.0 == 0
=> true

Maybe you're thinking of .eql?:

[5] pry(main)> 0.0.eql? 0
=> false

Edit: just observed that floats should be considered uneven for this, so I eat my words! Has the kata changed since it was originally written?