20 : 10 * 4 = 8 70 : 10 * 3 = 21 80 : 10 * 2 = 16 15 : 3 * 1 = 3 18 : 2 * 3 = 28

Решение:

1. \( 20 : 10 \times 4 = 2 \times 4 = 8 \)
2. \( 70 : 10 \times 3 = 7 \times 3 = 21 \)
3. \( 80 : 10 \times 2 = 8 \times 2 = 16 \)
4. \( 15 : 3 \times 1 = 5 \times 1 = 5 \)
5. \( 18 : 2 \times 3 = 9 \times 3 = 27 \)

Ответ: 8, 21, 16, 5, 27.