4. Посчитать в уме, разбивая делимое на 2 удобных числа 51:3 70:5 34:2 52:4 108:6 104:8 108:9

Решение:

1. 51 : 3
   \( 51 = 30 + 21 \)
   \( 30 : 3 = 10 \)
   \( 21 : 3 = 7 \)
   \( 10 + 7 = 17 \)
2. 70 : 5
   \( 70 = 50 + 20 \)
   \( 50 : 5 = 10 \)
   \( 20 : 5 = 4 \)
   \( 10 + 4 = 14 \)
3. 34 : 2
   \( 34 = 20 + 14 \)
   \( 20 : 2 = 10 \)
   \( 14 : 2 = 7 \)
   \( 10 + 7 = 17 \)
4. 52 : 4
   \( 52 = 40 + 12 \)
   \( 40 : 4 = 10 \)
   \( 12 : 4 = 3 \)
   \( 10 + 3 = 13 \)
5. 108 : 6
   \( 108 = 60 + 48 \)
   \( 60 : 6 = 10 \)
   \( 48 : 6 = 8 \)
   \( 10 + 8 = 18 \)
6. 104 : 8
   \( 104 = 80 + 24 \)
   \( 80 : 8 = 10 \)
   \( 24 : 8 = 3 \)
   \( 10 + 3 = 13 \)
7. 108 : 9
   \( 108 = 90 + 18 \)
   \( 90 : 9 = 10 \)
   \( 18 : 9 = 2 \)
   \( 10 + 2 = 12 \)

Ответ: 17, 14, 17, 13, 18, 13, 12.