I've assigned numbers to several European nations as shown below. My question is: what's my methodology in choosing these numbers? What would the numbers for Estonia, Latvia, and Lithuania be? (Note: I may have made a mistake, in which case I am sorry.) Portugal: 90 Spain: 90 United Kingdom: ...

The clockmaker took a walk after a lunch from a corner restaurant and found the old clock box with four similar looking clocks on every wall of the box. It is in the middle of the street intersection mounted on top of a tall wooden pole. "Can you restore and synchronize them?" ask an old man sitt...

Mr.K's message: It's a beautiful day outside! Geese are flying. Remember that my favorite seafood is squid? It's best served with Java waterdropwort! Let's eat them next time we meet, dad. Also note that, when I drink water, I always use a bowl made of a gourd. It's s...

222444 is the smallest number that is divisible by 2004 and only contains the digits 2 and 4. What’s the next number that has the same properties?

On the three paths of a station are A, B, and C types as shown in the figure. A locomotive driver (L) can attach from 1 to 9 trains to a locomotive at any one time, move them to the right path, and then move them to any left path. For example, if the locomotive picks up 2 trains from track n...

Let $n$ be a positive integer. You are given $4n^2$ kings and a $4n\times4n$ chessboard. You have to place the kings on the chessboard such that each row and column contains exactly $n$ kings, and no kings attack each other. How many ways can you do it? Pending Source

Sherlock is back in the city to solve mysterious cases. Currently, he is solving a murder case. The dead body is been sent to the forensic lab and now Mr. Sherlock is looking for some clues in the house where the murder took place. He found a door in the basement but unfortunately, it is locked b...

Find all functions $f:\mathbb{R}\rightarrow\mathbb{R}$ such that $$f(x)f(x+y)=xf(x)+f\big(f(x)\big)f(y)$$ for all $x,y\in\mathbb R$. Source: Problem by me. Functional equations are on-topic for this site.

I am a kind of tangle. But I don't look like noodles. I may look like a packet of noodle. I do not look like an entangled headphone. But I look more like a smartphone. What am I?