Well if Mathematics is your forte!
You take Two Mathematics in your Alevels ( Standard and Further )
And then you opt for Double Math in BS.C that lasts for 2 yrs.
Wouldn't you be competent enough to take on those two ?
I understand that Engineering wouldn't teach you purely maths as every engineering field have different sub topics , but they all may contains bits of Math.
The other subjects require some daily effort in my opinion, if you have a passion and interest, I think you can do them.
English especially, is something a CSS aspirant should daily strive to improve on.

Regarding the disclaimer, yes it's true... I don't know how can Mathematics help me in any CSS post apart from finance, but mathematics is an overall great tool that would come in handy at times in life, in my opinion.

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