Next challenge please!

The other day Darren found the index cards I had made for Nathan that were numbered from 1-10.  He put them all in order and asked if I would make some more number cards from 11-20.  I gladly made them for him and shuffled the entire stack.  He laid out all the numbers in numerical order.  I have not even been working with him and he continually surprises me.  He wants to learn and Nathan, for the most part, could care less.