1) 22 * 51 = 22 * (50 + 1) = 1100 + 22 = 1122
2)46 * 25 = 25 * (40 + 6) = 1000 + 150 = 1150
3) 5 * 109 = 5 * (110 - 1) = 550 - 5 = 545
4) 5 * 198 = 5 * (200 - 2) = 1000 - 10 = 990
5) 25 * 38 = 25 * (40 - 2) = 1000 - 50 = 950