need help on proration question

[Veronica Calvillo]

studying for real estate license exam and would like to take it soon but need some clarification on proration math probs and I've asked elsewhere but no one has been able to help me or clarify my confusion so am hoping that someone on here can. when it comes to prorating how can we determine if we need to prorate at the beginning of the yr or towards the end of the yr? for ex, if taxes are paid through the end of the yr and closing is on may 15 do we prorate from jan - may or from may-dec? and does it matter if taxes are paid in arrears or in advance when it comes to prorating? I've come across some proration probs where the actual months used were prorated and where the remaining months were used to prorate and this is what I need clarification for. for ex, annual taxes are 1600 for the calendar yr. seller prepaid through the end of the yr. if closing is on sept. 17 what amount will be prorated? so in this question the remaining months were calculated and am wondering why didn't they prorate from jan - sept.  would appreciate some clarification on this, thanks 

I would also like some feedback on how to use the amoritization table, thanks