Reversible Number Arithmetrick

Here's a nice fact from those NRICH folks again about reversible numbers.

Eggstreme

Awash with chocolate eggs and gift bags, confectionery delirium sets in and your mind starts to wander... Given you have 20 bags, what is the minimum number of eggs needed so that you have a different number of eggs in each bag? 
This puzzle and solution can be found here.
There is an interesting non-obvious (quite mischievous) solution which nicely illustrates what mathematicians can do when the rules are not overly defined.

Counting dots and squares

This was inspired by a similar problem in the Canadian Math Kangaroo Parent paper (2014).
You can see that paper here.