"I'm good at maths,...." I think that this English translation should drop the "s" on maths.

Bonjour Glen,
Je suis bon en maths, mais il est meilleur en maths que moi.
I'm good at maths, but he is better at maths than me.
Let's look at the Collins-Robert English to French translation of «math»:
math
(ˈmæθ )
noun abbreviation
(US) (= mathematics) maths fpl
So the French word is «maths». The first time I read this phrase, I too, found it disconcerting since we in the US do not say «maths», just the singular generic term «math».
Because it is written like that in the lesson, I am curious if this is a proper usage in other parts of the world.
Bonne chance et bonne continuation.

We say maths in the UK, that's probably why.

Bonjour Harriet,
Merci d'avoir donné une bonne explication.
Bonne chance.