1 for 5

I knew the girls were plotting something as we walked through the store.  They whispered to each other and kept disappearing to the next aisle.  The fact that they were leaving my side was my biggest clue.  The brunette twin still panics if we're in a store and I'm out of sight.  When she started going to the next aisle with her sister, I knew something big was going on.
They finally came to me with their big secret.  They really, really, really, really, really, really wanted a purple baby unicorn pillow pet.  Did I mention that they really, really, really, really, really wanted it?
I said, "No.  You have too many stuffed animals already.  Your father will not be happy if we bring home one more."
They were ready with a counter-attack.  The blond twin said, "We'll get rid of five stuffed animals if you buy us this one."  When I hesitated, the brunette twin said, "She means we'll get rid of five stuffed animals each."
We bought the pillow pet baby unicorn.  It seemed like a good deal to me.  We add one, remove ten and have a net loss of nine stuffed animals?  I'll take that deal.
Needless to say Daddy was not happy to see the new stuffed animal -- until the girls told him the deal.  They sealed it by saying, "We're going upstairs to sort out five animals each."  When they were done, they happily played with the new addition. 
We couldn't believe they came up with their own negotiating plan and then stuck to it.  They didn't complain about getting rid of the five stuffed animals each.  They didn't try to renegotiate.  They had a winning plan and they went with it.