2 is such a special number. The first prime number, the only even number that is also a prime, the answer for one of Zeno's Paradoxes, it has so many fascinating properties to itself that people don't always realise. In the current world filled full of instability, it's nice to have something that's definite and concise for once. Vi Hart goes through the various wonders of 2 with you in this short clip starring Brady Haran.
Models are one of the most challenging parts of Primary School Mathematics. They are very helpful for visualising (and solving!) the problem if done correctly, however getting there is half the battle itself. Here is an example to problem-solving via the modeling approach. (Credits to Yee Fook Siong)