Low health literacy: patients don't know how many pills they're taking each day?

Im reading an article on uptodate on "Heart failure: Self management". One passage reads:

--

For instance, while 71 percent of low-literacy patients in one study could read "Take two tablets by mouth twice daily," only 35 percent could correctly describe how many pills to take each day [15].

--

https://pubmed.ncbi.nlm.nih.gov/17135578/

Im kinda shocked by this finding. I mean, is that an issue of health literacy or simply basic math? That seems like a major hurdle if one would have to teach patients basic math and not just health literacy.

Any experience with this?

Author: princetonwu