1、
Starting from the condition of "from A to B at the same time, when the express train reaches the midpoint, the local train is still 20 kilometers away from the midpoint"
It is known that when the express train arrives at B, the local train distance B is still 20× 2 = 40km.
There is also: "When the express train arrived at B, the local train walked 80% of the whole journey."
Namely: "There is still 1-80% = 20% between the local train and B"
So: The distance between Party A and Party B is 40km/20% = 200km.
2、
Conditions: "70 pieces will be processed on the first day, and 1/3 of these parts will be processed on the second day".
It can be seen that it was processed two days ago: 70+ 1/3.
There is also: "At this time, the parts processed are 20 more than half of these parts."
That is, "processed two days ago": 20+ 1/2.
So: 70+ 1/3 = 20+ 1/2.
Simplified: 50= 1/6
So there are 50/( 1/6)=300 pieces in this batch.
three
Conditions: "Used 1/4, shipped 8 tons."
It can be seen that the current coal is (1- 1/4)+8, which is 3/4+8.
Conditional: "The ratio of tonnage to original tonnage at this time is 5: 4"
Available: (3/4+8): 1 = 5: 4.
The original solution is: 16 ton.