It only takes 1. When you "cum" in a girl, you relise about 1,000,000 sperm, but only 1, and sometimes 2 will reach the egg to fertilize it.

If you had unprotected sex, then yes. Being late doesn't nessisarily mean you are pregnant. It could be a lot of different things. A test will say negitive until you are a few weeks late. If a week or so later you still haven't gotten it, then get a ept.