>>9
"Math" and "maths" are actual words, "sci" is just an abbreviation and "scis" is just that abbreviation pluralized.
In common usage, "Math" is used by amerifags, whereas "maths" is used by brits and aussies. In common usage, they mean the same thing, serving as a shorthand for "mathematics".
In formal writing, "math" refers to mathematics in general and "maths" refers to multiple branches of mathematics. This is identical to the situation with "science", which refers to the field of science in general, and "sciences", which refers to multiple branches of science.
The reason the words "math" and "maths" exist is simply because
"mathematics" is already plural. You can't refer to multiple branches of mathematics as "mathematicses" nor can you retrofit "mathematic" for the job. Calling it "mathematics" in the first place was a short sighted 16th century mistake that took 300 years to fix.