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 ?
The largest possible difference occurs when
a b - c d =
98 - 21 =
77
Or.....if we are multiplying
a* b - c * d =
9 * 8 - 2 * 1 =
72 - 2 =
70
