Two baby rats unknown age

Question
QUESTION: I don't know the age of my two new baby rats. I bought them at a pet store. The rats are feeder rats. One of the rats is bigger than the other. I am not sure if the bigger one is a female the pet store said it was a female and it looks like a female according to websites. she also has a hole that looks like a vagina hole but she has a bump between that hole and her anus. how can I be sure she is a female. I am sure the smaller one is a female

ANSWER:   If they are young (around 4 weeks) it can be a bit difficult to tell their gender.  Male rats can tuck up their testicles when they are cold or stressed and it can make them appear as females.  The only way you can really tell is to look at lots of different pictures and compare your rats' bottoms to the pictures.  Here are some websites with good pictures to help you out:
http://www.thefunmouse.com/info/sexing.cfm
http://www.ratz.co.uk/sexingrats.html
http://www.afrma.org/sexing101.htm

 Generally the best way to tell is by anogenital distance, meaning the space between the anus and the genital papillae (that little bump that sticks out).  If the space is small, it is a female, and larger is the male.  If your two rats have a similar anogenital distance they are likely the same gender.  Hopefully those websites will help you out!  If you are still unsure you may have to get a veterinarian's opinion; if they are different genders you will end up with a litter of babies very soon so it is important to know for certain!  Good luck!

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QUESTION: so males have a hole right below where they go number 1

ANSWER:   No, males should only have an anus and a penis, with testicles between.  Females have a shorter gap between their anus and their urethra (which can look like a tiny penis) and right below their urethra is their vagina.  If your rats have a hole behind their urethra they are female.  The 'bump' you are seeing may be feces within her rectum ready to come out.

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QUESTION: sorry but do you know how to tell if a young female rat is pregnant like is there pictures with all the stages of a rats pregnancy. the reason is that the two rats were feeder rats and i am not sure if they were separated from the males and I want to know that they are not pregnant.

Answer
 Usually you can't tell that they are pregnant until the last week of their pregnancy, and sometimes you can't tell at all if their litter is small.  The first sign you will probably notice is the abdomen getting bigger, which is usually not apparent until the last week, but if you weigh them you may be able to track weight gain (though since they are young rats they will likely gain weight quickly anyway).  A few days before the birth the hair falls out around their nipples, making them more prominent.  They will also start to build elaborate nests, though some rats don't build a nest until after the babies are born.

 A rat's gestation period is 23 days, so if you wait that long after getting them and they show no sign of being pregnant then they probably aren't =)  If they are still babies there's a good chance they wouldn't get pregnant from the younger males still in the tank with them, but if there were older males, or your babies are over 6 weeks then there is a higher chance of a pregnancy occurring.  Just keep an eye on them and you should be able to see if their bellies get fatter.  I don't know of any websites with lots of different pictures but on this page on my website you can see a pregnant rat the day before she gave birth: http://www.evergreenrattery.com/careguide/pregnancy.html