Mathematics is a collective descriptor, leaving the 's' off the abbreviation implies there is only one field of mathematical study in the context of illiteracy in general it makes sense but not in the context of the specific condition described in the text (the word statistics is not abbreviated to stat).

Literacy relates to writing and reading so for the badge should either read.

"Illiteracy in the context of maths problems affects eight out of every five people" or

"Innumeracy affects 8 out of every 5 people" or

"Illiteracy specifically relating to sentences pertaining to the subject of math and innumeracy affects 8 out of every 5 people."