https://www.uiltexas.org/files/academics/White_NS2022SAC.pdf
Do all of this mentally in 10 minutes and see how you'd do on it. It must be so trivial for you.
This is literally a test for teenagers... and the ability to do it super fast isn't even math, it's trivial tricks...
If this is what interests you as a 15 year old, I think that's a fine hobby. If you're much over the age of 20 though...
I don't think even most adults know about mental math tricks
So if someone posts an "epic" mental math site, it's likely a kid.
(Adults don't use "epic" by the way)
Adults can use any words they want.