1. Weight of two bags of rice 168kg. Take out 3/4 of the whole bag of rice from the first bag and 2/3 of the whole bag of rice from the second bag. There is as much rice left in the two bags. How many kilograms of rice are there in these two bags? The first bag X and the second bag Y, according to the meaning: X+Y =1681/4x =1/3y; X=4/3Y is substituted into the above formula: 4/3Y+Y= 168 Y=72. X=96。

2. The sum of the ages of father and son is 63 years old, the age of father is 1/5, and the age of son is 1/2. How old are the father and son? Father+son =63 1/5 father = 1/2 son; Father =5/2 children; Substitute into the above formula: 7/2 sub = 63; child = 18； Father =45

3. Party A completed a project in 6 days, and Party B 10 days. Now Party A has completed13 of the total amount, and Party A and Party B have completed the rest. How many days can it be finished? X = (2/3)/(1/6+110) = 2/3 * 60/16 = 2.5 days.

4. For projects A and B, the number of the two teams should be adjusted due to work needs. Team A exchanges 1/5 of its own number with 1/4 of team B. After the exchange, the numbers of the two teams are equal. It turns out that the simplest integer ratio between Team A and Team B is (5/6) 4/5a+1/4b =1/5a+3/4b; 3/5a = 1/2b； A/B = 1/2*5/3=5/6

It takes 8 hours for the bus to go from A to B, and it takes 12 hours for the train to go from B to A. At present, two trains leave from two places at the same time. How long did the bus walk when they met? 3/5 buses complete the journey in 8 hours, with an hourly rate of 1/8. Similarly, the train completes the journey at112 per hour, and the two trains complete the journey at1/8+112 = 5/24.