There are 9 street lamps numbered 1 2 3 9 on the road

There are 9 street lights numbered on the road, each with a different number. These streetlights are spread across a straight road, and each street light is at an equal distance from each other. The road is a busy traffic artery with a large number of vehicles and pedestrians passing through on a daily basis.

These street lights play an important role at night, providing ample illumination for the road. Pedestrians and vehicles can accurately see the road ahead and avoid traffic accidents. Moreover, the presence of street lights also gives people a sense of security, especially when walking at night.

Each street light has a unique number, which is to make it easier for people to locate and navigate. When someone needs to indicate a specific location, they can determine their location based on the number of the street lights. This is especially important for out-of-town tourists, who can find where they want to go based on the number of the street lights.

These street lights are numbered from 1 to 9 in order. This arrangement not only facilitates people's navigation, but also makes the management of street lights simpler. When there is a street light that needs to be repaired or replaced, the staff only needs to operate in the order of the number, rather than the time-consuming and laborious search for a specific location.

In addition to numbering, these street lights have other features. They all use energy-efficient LED bulbs, which not only reduce energy consumption, but also extend the life of street lights. In addition, the brightness of the street lights can also be adjusted as needed to adapt to different weather and traffic conditions.

Overall, these 9 street lights on the road play an important role at night. They provide ample illumination to the road, allowing pedestrians and vehicles to travel safely. At the same time, their numbering and other features also make it easy for people to navigate and manage.

The presence of these street lights makes the road safer, more convenient and more comfortable.

You can't turn off the street lights at both ends, which means you can only turn off two of the four in the middle.

then there are c(2,4)=4 3 2 1=6 (i.e.: 23 24 25 34 35 45).

Because you can't turn off two adjacent ones at the same time, that is, you can't use 23 34 45, there are only 3 ways, i.e. 24 25 35

The street lamps have been arranged, so they cannot be solved by the method of arrangement, but can only be combined.

For example, if there are 10 street lights, turn off 2, and the conditions are the same as above.

Then there are: c(2,8)=8 7 2 1=28 species (2 consecutive trees are equal to the number of trees that can be closed minus 1).

Remove continuous (8-1=7 types).

There are 28-7=21 species.

Answer: 1 6

3 out of 10 lamps may be C(10,3) There may be 7 lamps that are not turned off, two lamps at both ends are not turned off, and the three lights that are turned off are not adjacent to each other, which is equivalent to inserting 3 lights turned off in 6 spaces between 7 lamps that are not turned off, using the plug-in method, it is c(6,3).

Therefore, the probability that the two lights at both ends are not turned off, and the three lights that are turned off are not adjacent to each other is:

c（6，3）/c（10，3）

Do you know how to pronounce one to one Qin?

dInsert 3 extinguished lights into 5 airs formed by 6 lights on, i.e., <>

It used to be a 9m lamp, but now it is a 12m lamp.

So find the least common multiple of 9 and 12.

is 36 so (250-1) 9 = 2 241 (m) because the number of lights is an integer, and all of them are less than the maximum value.

So there are 63 lamps that don't have to be replaced.

9*4=36, 36 is divisible by 12, so the ordinal number is ....The lights do not need to be moved (every four do not move).

250 4 = 62 and 2, so there are 62 + 1 = 63 lamps that do not need to be moved, and the serial number of the last lamp that does not need to be moved is 62 * 4 + 1 = 249.

The least common multiple of 9 and 12 is: 36

The total length of the route: (250-1) x 9 = 2241 meters.

2241 36 = 62 groups. The street lights that do not need to be moved for 1 meter are: 62 + 1 = 63 lights.

62x（36÷12）

62x3186 lamps.

The number of the last street light that does not move is: 186 + 1 = 187

Simple point introduction:

a a a a a

There are 5 A's on it, and there are 4 gaps between those five A's. The number of neutral gears +1=a is the "finding the pattern" problem in the first volume of the fourth grade, and the one ranked outside is equal to the one that is ranked inside plus 1

a___b＿＿＿c

In order to make "A, B, and C each have a street lamp", the greatest common divisor of 715 and 520 is 65, which is the spacing between the street lights. (715+520) 65=19 This is the total number of neutrals for this road divided by street lights. Because the street light is outside the neutral block, add 1 to get 20 street lights.

(300 6+1) 2,51 2,102 (lamps), A: A total of 102 lamps should be installed;

So the answer is: