"Okay," I sighed, picking up the invitation that was in front of me. "How many people have RSVP'd to Katie's surprise party on Friday night?""Out of the twenty-five people that we have invited, all of them have replied." My twin sister, Claire, informed."That's good." Giving my sister a thoughtful look, I asked, "So, out of the twenty-five guests that were invited, how many will be able to make it to the party?""Twenty-five.""That's good." I replied,...