Частина 1 — Вправи: 312

312. Прочитай рівності. Поясни, чому вони правильні.

9 + 1 = 10;	100 – 1 = 99;
109 + 1 = 10;	211 – 1 = 210;
10 – 1 = 9;	100 + 1 = 101;
110 – 1 = 109;	200 + 1 = 201;
99 + 1 = 100;	101 – 1 = 100;
210 + 1 = 211;	201 – 1 = 200.

315.

8 ● 9 – 7 ● 8 = 72 – 7 ● 8 = 72 – 56 = 16;

6 ● 5 + 5 ● 6 = 30 + 5 ● 6 = 30 + 30 = 60;

74 – 35 + 18 = 39 + 18 = 57;

65 + 15 – 44 = 65 + 5 + 10 – 44 = 70 – 44 = 70 – 40 – 4 = 30 – 4 = 26;

99 – 10 ● 9 = 99 – 90 = 9;

8 ● 0 + 8 ● 8 = 0 + 8 ● 8 = 0 + 64.