The chances of getting a girl pregnant would depend if the condom is uses correctly or not, because if its not the chances are probably 60-70% out of 100% but if used correctly the chances are 20%...
Some studies say about 10%. Condoms frequently fall off, are not used correctly or fail in so many ways. Some organizations would like you to believe that condoms=safe sex, but really condom use...
In general chances for pregnancy after unprotected sex are about 50%. But chances are increasing if unprotected sex happened i the middle of cycle and chances are decreasing if unprotected sex...
There are only a few days in every month when a person can get pregnant, so it all depends on when he ejaculated into you. However The best thing to do is have a look at the related link...