A classic story from my family.
My sister, visiting from Australia, decided to go into the card store to buy some postcards of the local scenery to send to her friends and family back home. The postcard display announced that they were 25 cents or 5 for a dollar, tax included. She selected 15 postcards she liked and presented them at the cash.
The cashier counted them carefully and announced that it would be $3.75. My sister said "But they're five for a dollar" and got the reply "But you have 15."
Frustrated, my sister pursued her line of argument. "You mean I could buy 5 for a dollar, go outside, come back in and buy the next 5 for a dollar, repeat once more and get the 15 for $3?"
"You can do it that way if you want" was the clever clerk's reply.
You can believe that this has become a catch phrase in my family: since each of us is always right in whatever we do, the sibling doing it differently is inevitably greeted by a chorus of "You can do it that way if you want" followed by peals of laughter.