I think the chances is 10 %

Yes, it is possible to get pregnant while on your period. Some women ovulate more than once during their cycle. Your chances are low, but the risk is still there.

What about if you take birth control and your on the "inactive" pills at the end of the month and its the day before your period?

Birth control pills prevent ovulation so, if you aren't ovulating, you can't get pregnant. Also, the follicular phase is, generally, more than 7 days long, so being without the pill for that length of time isn't likely to allow a follicle to develop to maturity.
Keep in mind, though, that nothing is 100% effective so, everytime you have sex, regardless of the contraception, you run the risk of pregnancy, even if only an slight one.