What are the chances of pregnancy if&?

What are the chances of pregnancy in the following case: sex on the last day of your period, condom (with spermicide) falls off and stays inside vagina (with sperm) for about 10 hours, douched right after sex?

It is hard to give you an exact percentage. Of course, there is always a chance of pregnancy whenever there is sexual contact (even if there is not penetration).

You were at a point in your cycle (assuming you are fairly certain about your cycle and it is regular) where fertility is relatively low, although not the lowest point. Having the semen presumably somewhat contained by the condom and having spermicide further lower your chances.

The only thing I advise against in the future is douching. Contrary to popular belief this does not wash the sperm out. Rather, it flushes them forward into the cervix and actually increases the chance of pregnancy.

Overall, I would say your chances are still fairly small.

REFERENCES
a listing of scientific articles and texts used.