a) 48 x 999 = 48 x (1000-1) = 48 x 1000 - 48 x 1 = 48000 - 48 = 47952
b) 547 x 999 = 547 x (1000-1) = 547 x 1000 - 547 x 1 = 547000 - 547 = 546453
c) 205 x 101 = 205 x 100 + 205 x 1 = 20500 + 205 = 20705
d) 123 x 1001 = 123 x 1000 + 123 x 1 = 123000 + 123 = 123123