That's easy. You always need one more roll than you bought. And you only find out after the shop closes. And if you do find it out before the shop closes, they are out of the pattern you picked.
Hey! That's brilliant. So, regardless of the size of the room, all I have to do is buy two rolls in the knowledge that if I had bought one, I would have needed one more but it wouldn't have been available to me!
Saves time and expense:)
Examine what is said, not who speaks.
"Efficiency is intelligent laziness." -David Dunham
"Think for yourself!" - Abigail