Teacher asks a kid how many dogs he would have if she gave him two dogs, then another two dogs?
The kid replies that they would have five dogs.
The teacher replies, no you're not listening. If I gave you two dogs then another two how many would you have?
The kid again gives the same answer - five dogs.
The teacher sighs and says OK if I give you two apples then a another two apples how many would you have?
The kid replies that they would have four apples.
Thank the lord, the penny has dropped exclaimed the teacher. So if I give you two dogs then another two dogs, how many dogs would you have?
Five replies the kid.
The teacher asks, "for the love of all that is holy how do you keep getting this answer you idiot"?
The kid says "I've already got one dog".