Teacher: “If I gave you 2 cats and another 2 cats and another 2, how many would you have? ”Johnny: “Seven. ”Teacher: “No, listen carefully… If I gave you two cats, and another two cats and another two, how many would you have?”
Johnny: “Seven. ”Teacher: “Let me put it to you differently. If I gave you two apples, and another two apples and another two, how many would you have? ”Johnny: “Six. ”Teacher: “Good. Now if I gave you two cats, and another two cats and another two, how many would you have? ”Johnny: “Seven! ”Teacher: “Johnny, where in the heck do you get seven from?! ”Johnny: “Because I’ve already got a cat!”
Source: weblovedogs.com