Students are knitting carves for fundraiser. Elaine can knit 4 scarves in 20 days. Mario can knit 2 more scarves than Elaine can in 40 days. What difference in the time it takes each of them to knit a scarf?

Elaine can knit 4 scarves in 20 days ... 4/20 = 1/5 of a scarf per day

Mario can knit 2 more scarves then Elaine can in 40 days ... so Elaine, if she knits 1/5 scarves per day, in 40 days, she can knit 1/5 (40) = 40/5 = 8 scarves. And Mario can knit 2 more ... so Mario can knit 10 scarves in 40 days ... 10/40 = 1/4 scarf per day.

so if Elaine can knit 1/5 of a scarf per day, it would take her 5 days to knit 1 scarf ... 1/5 * 5 = 1

and if Mario can knit 1/4 of a scarf per day, it would take her 4 days to knit 1 scarf ... 1/4 * 4 = 1

so the difference in time is 1 day ... because it would take Elaine 5 days to knit 1 scarf, and it would take Mario 4 days to knit 1 scarf