difference between Male and female RIR that are 8 weeks old??

[chick_magnet]

I bought 20 RIR straight run chicks from a guy. As of right now some have large comb and some have small. Some of the small comb chicks tails are have a bit of green. Does that mean its a rooster? Then I have one that is really light red. Does that mean its a hen. If so that means i got only one hen out of 20

. I guess what i am tryin to ask is what are some of the key different characteristics at 8 weeks for RIR chicks?
Also there are some chicks that has larger comb than the rest of the chick and its wavy and standing straight up its not fallin over. if i am describing it clearly

 

[justbugged]

The way I tell the difference between roos and hens at this age is their combs. The chicks with the bigger red combs are roos and the ones with the small pale combs are hens. I hope this helps.