91. 40:8 +2×100 40:(8+2)×100 (40:8+2)×100 100 - (40 + 36) : 4 100 - (40 + 36) : 4 100 - (40 + 36 : 4) 900:9-6×10 600:100+5×3 70×5+3×10

Решение:

1. $$40 : 8 + 2 \times 100 = 5 + 200 = 205$$
2. $$40 : (8 + 2) \times 100 = 40 : 10 \times 100 = 4 \times 100 = 400$$
3. $$(40 : 8 + 2) \times 100 = (5 + 2) \times 100 = 7 \times 100 = 700$$
4. $$100 - (40 + 36) : 4 = 100 - 76 : 4 = 100 - 19 = 81$$
5. $$100 - (40 + 36 : 4) = 100 - (40 + 9) = 100 - 49 = 51$$
6. $$900 : 9 - 6 \times 10 = 100 - 60 = 40$$
7. $$600 : 100 + 5 \times 3 = 6 + 15 = 21$$
8. $$70 \times 5 + 3 \times 10 = 350 + 30 = 380$$