ふん and ぷん, they don't mean the same 分【ふん】 (n) minute; (P). 分【ぶん】 (n,n-suf,pref) (1) part; segment; share; ration; (2) rate; (3) degree; one's lot; one's status; relation; duty; kind; lot; (4) in proportion to; just as much as; (P). 分【ふん】is minute, it is used for time. In Japanese, the number 4, 7 and 9 have two different pronounciations but both pronounciation means the same. Here the 9 is pronounced in either きゅう or く. So, nine o'clock is either きゅう じ or く じ.

Hi Elizabeth, If the number has staccato sound little 'っｔｓu' or ending 'んn', you use ぷん. ex. ippun いっぷん 一分 sanpun さんぷん　三分 yonpun よんぷん 四分 roppun ろっぷん 六分 happun はっぷん　八分 juppun じゅっぷん　十分 juippun じゅういっぷん　十一分 ... i hope this makes easier for you!

ah.... It's difficult ... Even Japanese children sometimes take a mistake about the difference , so parents need to correct them into right pronunciation. I memorized the pronunciation to count in my bath and in the pool when I was child . and play tag. The following page looked like useful :] http://www.reikialoha.com/bbs/learning-japanese/000019-000000

I know little about Japanese,and i think that there are some words which just don't change regularly. So the only way to remember them is reciting.