1. 40 7/30 - 38 5/12 = 1207/30 - 461/12 = 2414/60 - 2305/60 = 109/60
2. 7/8 - 7/30 = 105/120 - 28/120 = 77/120
3. 77/120×1 9/11 = 77/120×20/11=(77×20)/(120×11) = 77/660
4. 109/60÷10. 9 = 109/60÷10 9/10 = 109/60÷109/10 = 109/60×10/109 = (109×10)/(60×109) = 10/60 = 1/6
5. 77/660×4.2 = 77/660×4 2/10 = 77/660×42/10=(77×42)/(660×10)=3234/6600
6. 1/6+3234/6600=(1100+3234)/6600 =4334/6600 = 723/1100
7. 723/1100÷0.008 = 723/1100÷8/1000 = (723×1000)/(1100×8)=723000/8800=83