Short trick:
D1 = X – 100 and D2 = Y – 100
Then product of X and Y
(X+D2)x100 + (D1xD2) OR (Y+D1)x100 + (D1xD2)
Multiply 97 and 104
Solution:
D1 = -3 and D2 = 4
Then
(X + D2)x100 + (D1xD2)
=(97 + 4)x100 + [(-3)x4]
=(101)x100 + (-12)
=10100 – 12
=10088