"She usually reads two books each month."
Translation:Ŝi kutime legas po du libroj monate.
Po seems more to mean "at a rate of". The dictionary I looked at says it is a noun but ... to me seems to act more like an adverb. "Reads at a rate of" or "costs at a rate of".
Yeah, but it's each month, right, not each two books. A real pain, this po.
It comes form Polish "po". In Polish: Ona zwykle czyta (po) dwie książki miesięcznie. In Esperanto: Ŝi kutime legas (po) du libroj monate. But it seems that without "po" the sentance would also be understandable. Besides, you can also say: "Ŝi kutime legas du librojn ĉiumonate"
It's a bit like German 'jeweils', I guess, though you would leave that out more often than not.
Kial "Sxi kutime legas du libroj monate" malpravas? Bonvolu, ekspliki min. Mi neniam vidis la vorton "po"!