Perhaps those 40 problems were supposed to be easy? If it was all arithmetic perhaps it was just for developing speed? If the child is comfortable with it would not take that long.
I think language is a major problem but also culture, you do not see Asian kids having same problems that kids from South/Central America do, why I have no idea to be honest, but it does seems to be the case.
Too much of the homework kids are given is busy work. Writing a word 100 times they can already spell, word searches in a matrix of letters (what the heck does that teach?), circling any word that represents a type of rock on a page of print, etc. I found about 5 minutes of learning in 5-6 hours of homework.