Sharpening The Chess Mind

IT is said that keeping your mind sharp helps your chess.
I guess it would be hard to prove that it doesn't help, but how does one actually keep a mind sharp?
I don't know, but one thing I do do is fill in idle moments on the Tube or train by trying to make a balanced equation out of a carriage's number (this is normally displayed at each end of the carriage).
Today, for example, I went by Tube from Moorgate in Central London to Colindale in North London, incidentally visiting the RAF Museum (entry is free).

An RAF Xmas

My journey was on the Northern Line.
One carriage had the serial number 51574.
Making a balanced equation out of this - each number should be used once and once only, and must be added, subtracted, multiplied or divided - is rather easy.
*****
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51574
One solution is: 5+1+5=7+4
Not much of a challenge there, but the other carriage was much more difficult, at least for me.
51649
*****
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I finally cracked it: (6-4)x5=1+9
Will doing this really improve my chess? I doubt it, but I find it fun and it surely cannot hurt.