Did you perhaps watched the movie 'Gifted' ?
Chris Evans and Mckenna Grace had done remarkable work in this film. The main lead is little girl named 'Mary' portrayed by Grace . She has the role of a kid with knowledge more than any mathematician of this era.
The main topic of my above question is , there is this small scene in this movie , where they have mentioned doing calculation with the help of Hitler’s method ( no offence Jews ) known as Trachtenberg method . In today’s time we have many ways to calculate a simple 2+2 , like by Vedic maths, Abacus , our regular maths(conventional method) etc.
Trachtenberg method were used in war camps during world war II , by the soldiers to keep calm and focused . After that this method is used by many but doesn’t have that lamelight. If you want to improve your mental strength in mathematics give this method a try maybe your end result would be more than you expected.
Try YouTube videos for this maths . I wish you all the best.
(Note : this is my first story on medium , and it’s not the best but i did what I can )