"Average speed" relationship between the number of line test this little thing

2020 has kicked off in February, the pace of provincial exams be far behind? I believe that many candidates have begun to prepare for the provincial exams. The line test as an important part of the provincial exams, will undoubtedly need to spend a lot of time to practice, which, measured in the line travel problems occur at higher frequencies, it can be described as the darling of the number of relationships, but because of their difficult, but it is big most abandoned child candidates. In order to make the trip is no longer a question everyone's weakness, we learn together next trick them - the problem formula Solving travel.
Since it is a problem-solving formula, then, what is the formula we are dealing with today, is it? The problem is often used in stroke average speed formula, that if two equal distance, the distance of these two average speed (which were traveling speed on these two away). Therefore, the trip was involved in a journey equality and the need to solve the speed, you can consider the application of this formula to solve.
As described in this example channel:
[Example 1] from A to B 111 km. There is a flat road, uphill, downhill. It is assumed that a vehicle speed flat road is 20 km / h, the speed is 15km uphill / downhill speed is 30 km / h, the vehicle A to point B by the round trip the average speed is how much?
When A.19 one thousand meters / B.20 km / C.21 km / D.22 km / h
[answer] B. Parsing: B. Method One: Solving round trip average speed, the first thought is solved by the total distance divided by time. The total round trip distance of 111 × 2 = 222 km and the total round trip time was go flat road, uphill and downhill and adding time, the respective time is divided by the distance corresponding to the respective speeds can be obtained. Uphill and downhill at A to point B, becomes the return uphill and downhill, thus, the total distance uphill and downhill are total distance, total distance of a flat road, the average speed km / h . Select B.
Method two: round trip time, and the slope of decline took an equal distance, average speed applications available on the downhill formula an average speed of km / h, while flat road speed is 20 km / h, therefore, from a round trip to point b should be the average speed 20 km / h, select B.
Contrast the above two methods is not difficult to find, the first method the computational complexity is not easy to solve, the second method appears to be much easier, you can do to improve the speed problem. We then consolidate a question about the following:
[Example 2] Xiao Ming from A, the need for a flat road and then go on to some slope to B, B to the ground, where he stayed one hour to backtrack A. When Bob to go when flat road speed in kilometers / uphill speed of 4 km / h the downhill speed of 8 km / h, Xiaoming departure from the common returns to seven hours, then the distance A, B is two ()km.
A.10 B.12 C.15 D.16
[answer] D. When returned from the departure point to the downhill walking distance equal to the average speed of km / h, flat road travel speed is km / h, i.e. the equivalent of speed km / 2 times the whole of the left, with: parsing 7-1 = 6 hours, then the distance a, B is two kilometers, select D.
By analyzing the above subject, the average application rate formula must meet a prerequisite - an equal distance. Therefore, we must bear in mind that this precondition and memorize formulas, later encountered similar problems on the trip can use this technique to quickly solve problems.