19 skeins of yarn* (1 scarf/ 3.5 skeins of yarn)= 5.429 scarfs.
Because there is not enough yarn to knit 6 scarfs (with 19 skeins of yarn, we can only knit 5.429 scarfs) and the number of scarfs has to be a natural number, Delia can complete 5 scarfs if she has 19 skeins of yarn.
Hope this helps~
