Can the zookeeper put one cage inside another?
When you add two even numbers you get an even number and when you add two odd numbers you get an even number, so adding four odd numbers together will give you an even number as well.
So there must be a trick to the question and you will have to try some lateral thinking. There may be many assumptions that you could reject. I wonder if one cage can be inside another...?
Stephen La Rocque.>