The national civil service examination channel provides answering skills for the 20 19 national examination, including answering skills for quantitative relations of test questions, mathematical operation, numerical reasoning, mathematical formulas and other quantitative relations. Get a quantitative relationship, is it still? No, we can see the answer as long as we look, and we can see the result when we look. Among the ever-changing topics, there is a kind of topic that will describe an event in two ways. At this time, we only need to write two plans and have a look to see the results.

Sample demonstration

Example: 1: The fruit shop sells one kilogram 10 yuan, 12 yuan and 16 yuan every day, and the income is *** 100 yuan. It is known that the income of fruits sold per kg 12 yuan and kg 16 yuan is 10/6 yuan, so the fruit sold per kg10 yuan is () kg.

A.26 B.30 C.34 D.38

For this problem, the first thing some students may think of when they get their hands on it is to list the equations. Assuming that the weights of X, Y and Z are 10 yuan, 12 yuan and 16 yuan respectively, we can get the following three equations: x+y+z= 100,/kloc-. Then solve the equation and the answer comes out, but the actual time is not that much. Yes, there is basically only one exam left. We might as well come up with two conditions in this question: the * * * income of the three prices is 13 16 yuan, in which the fruit per kilogram 12 yuan and the fruit per kilogram 16 yuan * * * income is16 yuan. Then, isn't the price difference in 300 yuan just per kilogram 16 yuan?

Advanced method

Example 2: A batch of parts, if all are handed over to a factory for processing, will be completed within the planned time; If it is all processed by factory B, it will take more than 5 days to complete. If factory A and factory B cooperate to process for 3 days first, the rest will be processed by factory B alone, just within the planned time. The planned processing time of this batch of parts is () days.

A.5 B.7 C.7.5 D.8.5

This topic is an engineering problem, and we know that if we find the total workload, or work efficiency ratio, we can make an answer soon. But according to our observation of this problem, the completion time of separation is not much, so we can't use special values. So can we find the efficiency ratio? Obviously, there is no direct. But let's analyze the following words: if all of them are processed by factory B, it will take 5 days longer than planned, that is, the time required for B to complete is planned time+5; Let's look at this sentence again. If factory A and factory B cooperate to process for 3 days first, and the rest is processed by factory B alone, it will be completed according to the planned time, that is, factory B can complete it in 3 days after making a planned time. Comprehensive comparison, that is, 5 days of B is equivalent to 3 days of A, and the efficiency ratio of A and B is 5: 3, so let A's efficiency be 5, B's efficiency be 3, and the planning time be 3×5÷(5-3)=7.5 days.

Let me show you another question:

Example 3: Both parties need to check their luggage. The consignment fee is less than 10kg 6 yuan /kg, and the fee per kg for the part exceeding 10kg is slightly lower. It is known that the freight charges of Party A and Party B are 109.5 yuan and 78 yuan respectively, and Party A's luggage is 50% heavier than Party B's ... Then, the charging standard per kilogram for the part exceeding 10kg is () yuan lower than that within 10kg.

A. 1.5 B.2.5 C.3.5 D.4.5