There are usually 2 numbers on a runway, one for each end of it.
They seem like random numbers but here is a simple math to relate them.
This video shows only how to figure out the number of the other end of the runway.
I would make a separate video to explain the actual meanings of runway numbers sometime in the future (hopefully ;).

Disclaimer:
This video was not made or reviewed by either a pilot or an aviation expert. So the information in this video might not be accurate or correct. I made this video for my record in the process of learning flying in flight simulators and hopefully someone would find this video useful or maybe entertaining.

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This video "Airport Runway Numbers Explained! (Part 1)" was created under Microsoft's "Game Content Usage Rules" using assets from Microsoft Flight Simulator, and it is not endorsed by or affiliated with Microsoft. Microsoft Flight Simulator © Microsoft Corporation. Microsoft's "Game Content Usage Rules" link: https://www.xbox.com/en-US/developers...

This video "Airport Runway Numbers Explained! (Part 1)" is not endorsed by or affiliated with Boeing, Airbus and/or anything in this video.

This video was created using screen recordings of the game Microsoft Flight Simulator for entertainment purpose only and is not what happened in real life.