5. If Nintendo made a handheld that was able to play every handheld cartridge game they ever made how many different physical cartridge slots would this handheld need?
Ooh, tricky. Never had a Gameboy Advance. Let's see - original GameBoy and GameBoy Colour makes for one. Advance makes for two. DS/DSi makes it three.
Thing is, I can't really recall whether the Advance uses the same physical cardridge format as the original GameBoy. If it does, then the answer is a mere two, and in fact the original DS has it. If it doesn't, the answer is three.
And here Wikipedia gives the answer, it is three:
The Nintendo DS is backwards compatible with Game Boy Advance (GBA) cartridges. The smaller Nintendo DS game cards fit into Slot 1 on the top of the system, while Game Boy Advance games fit into Slot 2 on the bottom of the system. The Nintendo DS is not compatible with games for the Game Boy Color and the original Game Boy, due to a slightly different form factor, voltage requirements, and the absence of the compatibility mode. The Sharp Z80 compatible processor used in the older systems is still included, and indeed necessary for some GBA games that use the older sound hardware.
http://en.wikipedia.org/wiki/Nintendo_DS