Cockerel or Hen? New to Raising Backyard Chickens

[fdimeo]

My fiance and I ordered 10 unsexed Isa Brown chickens from Tractor Supply. We're having some difficulties distinguishing whether we have cockerels or hens. In doing some research, we believe there may be 7 cockerel's in this group, so we're hoping anyone on these forums can assist in distinguishing them. There were 7 yellow chics, one of which grew black feathers and speckled (1st picture), the others stayed yellowish. The brown ones we believe are hens. Please help! Do I have 7 cockerels and 3 hens?

 

[The Happster]

First 5 pics are cockerels.
The brown birds are pullets.

 

[HappyClucker7]

Yes, all the white ones are cockerels.

 

[chickenlittle21]

All the white ones are cockerels. The brown ones are pullets. The one in the first picture is a cockerel.