См скрин
===========================
Как понять таблицу сложения ?
12-4=8
11-6=5
10-3=7
10-8=2
12-5=7
11-7=4
39 = (30 + 9) : 3 = 10 + 3 = 13 13 * 3 = 39
52 = (40 + 12) : 4 = 10 + 3 = 13 13 * 4 = 52
84 = (42 + 42) : 2 = 21 + 21 = 42 42 * 2 = 84
75 = (50 + 25) : 5 = 10 + 5 = 15 15 * 5 = 75
91 = (70 + 21) : 7 = 10 + 3 = 13 13 * 7 = 91