Answer by Neil Menon:
Well, this is not exactly a teacher-student lesson, but a lesson which put me right in my place. I'm a physicist and have a solid base in mathematics. So when my younger brother asked me to solve this, I took one look at the problem and blurted instantly: "oh come on, man! You find this crap hard? Try solving Schrodinger's equation to start with!""Just solve it, Neil!" He insisted.I was at my usual coffee shop, having breakfast and was a little annoyed at the way I was interrupted. Nonetheless, I decided to switch on my Show Off Mode and solve the damn thing.I grabbed a tissue paper that the waiter had given me and scribbled him the answer and sent it through Whatsapp. As soon as it got sent, I sat back and smiled, quite content and proud with the answer that I had given him.So, here's the questionAnd here's my answer:Well, 3 unknowns and 3 simultaneous equations, piece of cake, right?Half an hour later my brother messaged me back.Noel (My Brother): Shit, man! What a nerd! I totally see the physicist in you taking over.Me (gloating with pride): So, did you get it?Noel: Sure did! But I solved it in a different way.Me: Aaaaannd you got the same answer?Noel: Yes, I did!Me: Wow, really?Noel: Well, all the figures appear twice in the first three diagrams and if you add them all up you get, 2(x+y+z) = 10 + 20 + 24 = 54. So x+y+z = 54/2 = 27!Me (my pride nosediving): Hey, that's not bad!That's the day I realized there's always a simpler explanation to everything. You just need to keep your mind and ears open to get it!