Do you think I'd work on a pair like that?

I tried on a pair and looked in the mirror.

Keep an eye on the pair, and wait; nothing would be lost by going slowly in so important a matter.

"Need any help keeping an eye on the pair of them?"

Take your time and try on several pairs until you are certain they will be comfortable.

Let's say you're in a department store trying on a new pair of pants.

Then he pulled on a pair of pants and left the room.

"Now what the devil do you mean by trying on a pair of those things?"

And I think she must have had on a pair of trousers.

Billy kept an eye on the pair of them and followed me.