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?

PLS HELP

Guest Dec 20, 2018

#1**+1 **

a*b will be largest when a = 9 and b = 8 [or vice-versa]

c*d will be smallest when c =2 and d =1 [ or vice-versa]

So

The largest possible difference is

9 * 8 - 2*1 =

72 - 2 =

70

CPhill Dec 20, 2018