Решение:
1. Примеры:
- 1) \( 40 : 2 = 20 \)
- \( 70 : 2 = 35 \)
- \( 80 : 2 : 5 = 40 : 5 = 8 \)
- 2) \( 50 : 10 + 15 = 5 + 15 = 20 \)
- \( 28 : 4 + 43 = 7 + 43 = 50 \)
- \( 80 : 1 - 25 : 5 = 80 - 5 = 75 \)
5. Примеры:
- 1) \( 13 \cdot 7 = 91 \)
- \( 23 \cdot 3 = 69 \)
- 2) \( 18 \cdot 4 = 72 \)
- \( 3 \cdot 29 = 87 \)
- 3) \( 6 \cdot 16 = 96 \)
- \( 20 \cdot 5 = 100 \)
Ответ: 1) 20, 35, 8; 2) 20, 50, 75; 1) 91, 69; 2) 72, 87; 3) 96, 100.