Вычислите, используя приём быстрого вычисления. 4 •49 = 1• (50 - 1) = 4 • 50 - 4•1 = 200 - 4 = 196

7 • 89
5 • 68
8 •29

39 •3
48 • 6
79 • 7

5 •78
4 •99
9 •39​

Пошаговое объяснение:

1)  7 * 89 = 7 * (90-1) = 7 * 90 - 7 * 1 = 630 - 7 = 623

2) 5 * 68 = 5 * (69-1) = 5 * 69 - 5 *  1= 345 - 5 = 340

3) 8 * 29 = 8 * (30-1) = 8 * 30 - 8 * 1 = 240 - 8 = 232

4) 39 * 3 = 39 * (4-1 )= 39 * 4 - 39 * 1 = 156 - 39 = 117

5) 48 * 6 = 48 * (7-1 )= 48 *7 - 48 * 1 = 336 - 288  = 48

6) 79 * 7 = 79 * (8-1) = 79 * 8 - 79 * 1 = 632 - 79 = 553

7) 5 * 78 = 5 * (79-1) = 5 * 79 - 5 * 1 = 395 - 5 = 390

8) 4 * 99 = 4 * (100-1) = 4 * 100 - 4 * 1 = 400 - 4 = 396

9) 9 * 39 = 9 * (40-1) = 9 * 40 - 9 * 1 = 360 - 9 = 351