minored in math, yet I cannot count

Realized yesterday that if x = the 4 skeins I bought, m =a less than half done clapotis, and b =the 3rd skein of yarn that is almost used up, that y = me rummaging through the shelf at the yarn store to find the remaining 3 skeins that she has in stock. I think I misread the yarn requirements on one of the entries on the yahoo clapotis KAL database. Or I lost my ability to do simple multiplication. Or both. I haven't checked the lot numbers to see that they are the same. My current delusions are: 1)With this type of pattern and a varigated yarn, the color differences wouldn't be noticable and 2)A small yarn shop would only have skeins from a single dye lot.