Mathematical problems in quantitative relations, mathematical problems in primary and secondary schools, and mathematical problems in primary schools are the main ones. It is not too difficult to test professional knowledge and thinking.

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Question reference:

1. It takes 10 days for Party A to complete a project alone, and 15 days for Party B to complete it alone. If both parties cooperate, how many days will it take?

A.5 B.6 C.7 D.8

2. A city has three engineering teams, A, B and C, and the work efficiency ratio is 3: 4: 5. It takes 25 days for Team A to complete Project A alone, and 9 days for Team C to complete Project B alone. If three engineering teams cooperate, how many days will it take to complete these two projects?

10 D. 12

3. A farm has 36 harvesters, and it takes 14 days to harvest all the wheat. Now harvest for 7 days and add 4 harvesters. Through technical transformation, the efficiency of each machine is improved by 5%. How many days does it take to harvest all the wheat?

A.5 B.6 C.7 D.8