How to read Russian

I know how to read 1/3 1/2 etc but how to read 2/2.5 and mathematical formulas such as 2/(1+3)?

Some say it's possible to read 32.1 as тридцать два и одна it's ok to read 5.6 as пять и шесть? how about really long numbers such as 1.23456? the formal way...

how to read latin alphabets in russian texts? for example chemical symbols or chord names in music? Do I read them according to their English pronunciations?