Question

If a, b, c, and d are replaced by four distinct digits from 1 to 9, inclusive, then what's the largest possible value of the difference a.b - c.d ?

Answer 1

Maximize ab-cd.
So, we want to make ab as large as possible and cd as small as possible.

ab = 9*8 (the two biggest allowed) = 72
cd = 1*2 (the two smallest allowed) = 2

72 -2 = 70

hope this helps :)