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Help ~ There are six elementary school math problems. Find the solution of proportional knowledge. Write down the process, preferably why ~ thank you.
1.254.5kg Let the total mass of oranges be xkg, then the total mass sold in two days is: 40% x+140 = 0.4+140; The total mass of the remaining oranges is (1-40%) x-140 = 0.6x-140; So there is: (0.6x-140)/(0.4x+140) =1/3, and x=254.5kg is calculated.

2. 16m Let Rabbit A be x meters away from the finish line. Because the two rabbits advance at a constant speed, the distance they run in the same time is proportional: 40/50 = (80-x)/80; X= 16m, that is, the distance from rabbit A to the finish line is 16m.

3.56.25KM If the distance between Party A and Party B is X, the time for the ship to travel from Party A to Party B is X/25h, and the time for traveling from Party B to Party A is x/ 15h, the total time is X/25+X/15 = 6; Find x=56.25KM.

4.30 days because I read 1/7 in the first five days, so the remaining 6/7 needs: [5/( 1/7)]*(6/7)=30 days.

The design of 5.24 days actually took X days to complete. The original planned number of parts per day was 12000/30=400, but the actual number of parts per day was 400+ 100=500, so x*500= 12000 is x=24 days.

6.42. It takes X people to complete the current plan. According to the original plan, the total project quantity is 35 *18 = 630; Then according to the current scheme x*( 18-3)=630, x=42 people are obtained.