640 is unacceptable for any decent school, no matter MBA or PHD,don't waste ur money to some junk schools.
Recite JJ and take it again, sometimes Test is only correlated with Luck. The 1st time I took GMAT only got score of 650 and one month later, I took it again and got 720. I don't see too much improvness in one month. In the test, I still couldnot figure out what is the helk with this question. The only diff between these 2 tests is I recite JJ and I'm lucky.