A young woman decided to redecorate her bedroom. She wasn't sure how many rolls of wallpaper she would need, but she knew that her friend next door had recently done the same job and the two rooms were identical in size.
"Buffy," she said, "how many rolls of wallpaper did you buy for your bedroom?"
"Ten," said Buffy.
So the girl bought the ten rolls of paper and did the job, but she had two rolls leftover.
"Buffy," she said, "I bought ten rolls of wallpaper for the bedroom, but I've got two leftover?"
"Yeah?" said Buffy, "That's funny, so did I!"