What number of reasons can you justify for the rbc count in males being higher than that of females?

Just a couple...: Women often menstruate every month, causing a loss of blood, and therefore, a lower RBC count. Furthermore, women often become iron-deficient (partially because of menstruation as well), and this can lead to a state of anemia or near-anemia. Men, in my experience, are also more likely to respond to sleep apnea by increasing RBC count, so this might also explain. There are a few, at least.

Homework problem: I would not assign this question. After puberty, men have considerably more testosterone than do women and this promotes the growth of red blood cells. Women have periods and thus tend to lose iron, and pregnancy depletes iron and folic acid, and a woman may thus be anemic as a result. However, this should not happen. The major reason is testosterone. I hope this is the answer teacher wants.