Customers And Math: Always The Same Old Yarn

(I work in a shop that sells yarn and knitting supplies. A lady has come in and spent some time looking at our yarn, and since she looks a little puzzled, I go over and ask if I can help. Yarn is usually sold by weight, in skeins of 50 or 100 grams, and knitting patterns tell you how many grams of yarn you need.)

Me: “Can I help you find anything?”

Woman: “Yes, I was wondering if you have really large skeins of dark-grey yarn.”

Me: “I’m afraid these are the only dark-grey yarns we have.” *pointing at different kinds of yarn in 50-gram skeins*

Woman: “That’s such a shame. I have a pattern that says I need 450 grams of yarn! Fifty is definitely not enough.”

Me: *desperately trying to keep a straight face* “You could just get nine 50-gram skeins.”

(It took her at least a minute to work that out!)