(Устно.) Вычисли.
42 : 3;
18 * 4;
60 : 5;
27 * 3;
36 : 2;
19 * 5;
91 : 7;
46 * 2;
72 : 3;
35 * 2;
84 : 3;
39 * 2.
42 : 3 = (30 + 12) : 3 = 30 : 3 + 12 : 3 = 10 + 4 = 14;
18 * 4 = (10 + 8) * 4 = 10 * 4 + 8 * 4 = 40 + 32 = 72;
60 : 5 = 12;
27 * 3 = (20 + 7) * 3 = 20 * 3 + 7 * 3 = 60 + 21 = 81;
36 : 2 = (20 + 16) : 2 = 20 : 2 + 16 : 2 = 10 + 8 = 18;
19 * 5 = (10 + 9) * 5 = 10 * 5 + 9 * 5 = 50 + 45 = 95;
91 : 7 = (70 + 21) : 7 = 70 : 7 + 21 : 7 = 10 + 3 = 13;
46 * 2 = (40 + 6) * 2 = 40 * 2 + 6 * 2 = 80 + 12 = 92;
72 : 3 = (60 + 12) : 3 = 60 : 3 + 12 : 3 = 20 + 4 = 24;
35 * 2 = (30 + 5) * 2 = 30 * 2 + 5 * 2 = 60 + 10 = 70;
84 : 3 = (60 + 24) : 3 = 60 : 3 + 24 : 3 = 20 + 8 = 28;
39 * 2 = (30 + 9) * 2 = 30 * 2 + 9 * 2 = 60 + 18 = 78.