Explanation: It takes 20 hours for an express train to go from A to B, which means it takes 65438+ 0/20 of the whole journey per hour. This is its speed. So is the local train. The total distance is regarded as "1".

Sum of distance/speed = meeting time

○2 1/6 ...10 of Party A and Party C should be112 of the total of Party A and Party C.

The following results can be obtained: a work efficiency +B work efficiency = 1/6.

B+C = 1/ 10

A work efficiency +C work efficiency =112.

Total efficacy of three people: (1/6+110+112) ÷ 2 = 7/20.

Time required: 1 ÷ 7/20 = 20/7 (days)

○3 The first question; With the second question

A work efficiency +C work efficiency =1÷15/2 = 2/15.

A work efficiency +B work efficiency =160/7 = 7/60.

Ergonomics B+ Ergonomics C =120/3 = 3/20

Mathematics: 1 is the total amount of work, and the total amount of work ÷ working time = working efficiency.

Total efficacy of three people: (2/15+7/60+3/20) ÷ 2 =1/5.

Time: 1 ÷ 1/5 = 5 days

Work efficiency. Efficiency A = total efficiency-efficiency b/c and =1/5-3/20 =1/20.

A Time taken: 1 ÷ 1/20 = 20 days.

Efficiency of B = efficiency of A and B and efficiency of -A = 7/60-1/20 =115.

Time:1÷115 =15 days

Efficacy of C: A-C ergonomics and -A ergonomics = 2/15-1/20 =112.

Time:1÷112 =12 days

So: Party A needs 20 days, Party B needs 15 days and Party C needs 12 days.