Estimated difference of 7 17/20 - 6 2/5

Is always easier to subtract or add fractions with the same denominator, so

6 2/5 is the same as 6 8/20

I would suggest turning them both to improper fractions,

(You multiply 6 by the denominator 20 and get 120 then add 8)

6 8/20 = 128/20

and then do the same with 7 17/20 (Mutiply 7 and 20 and then add 17)

7 17/20 = 157/20

157/20 - 128/20 = 29/20 or 1 9/20