This solution assumes that the original total amount of brine is x.
40%x=(80+x)*30%
x=240
240+80 = 320kg saline: 320 * (1-30%) = 224kg.
The total amount is: 224/50% = 448kg.
Therefore, to add salt is: 448-320= 128 kg.
2. Two cars, Party A and Party B, are driving in opposite directions at the same time, and meet at a distance of 68km from Party B. After each car arrives at the other station, it immediately returns to its original place and meets at a distance of 52km from Party A on the way. Find the distance between the two places.
Answering the first encounter, the two walked a whole journey and walked 68 kilometers for the second time.
When they met for the second time, they walked three full distances, so B should have walked 68*3=204 kilometers.
In fact, B walked the whole distance, adding 52 kilometers.
So the distance between the two places is: 204-52= 152 km.
3. Two cars, A and B, leave from two places along the expressway at the same time. The average speed of car A is 48 kilometers per hour, and that of car B is 54 kilometers per hour. When they met, the distance between the two cars was 36 kilometers. How many kilometers are the two places apart?
When we met, B was greater than A: 36 * 2 = 72km.
There is more than one line in Otsuichi time: 54-48 = 6km.
Therefore, the meeting time is 72/6= 12 hours.
The distance between the two places is:12 * (48+54) =1224km.