There are 40 street lamps in one place, and there is an advertisement between every two lamps, so ho

Assuming there are 40 street lights, we can use a line segment to represent these 40 street lights, and the two ends of the line segment represent the first and 40th street lights respectively. Now we need to insert an ad on this line segment, one between every two street lights.

We can divide this line segment into 39 segments, each representing the distance between two street lights. We need to insert ads in these 39 segments.

Let's say we insert an ad in the first segment, then the number of ads we need to insert in the remaining 38 segments becomes 38.

By the same token, if we insert an ad in the second segment, the number of ads we need to insert in the remaining 37 segments becomes 37.

By analogy, we can get a pattern: for each ad inserted, the number of remaining segments decreases by 1.

So, we can get the total number of inserted ads as: 39 + 38 + 37 + 3 + 2 + 1.

This is a summation problem of an equal difference series, and we can use the sum formula for an equal difference series to calculate.

The formula for summing the difference series is: sn = (a1 + an) *n 2, where sn is the sum of the difference series, a1 is the first term, an is the last term, and n is the number of terms.

According to the nature of the difference series, we can get that the first term a1 is 39, the last term an is 1, and the number n is 39.

Substituting these values into the equation of summing the difference series, we can get the total number of inserted ads as: (39 + 1) *39 2 = 780.

So, there are a total of 780 ads.

There were a total of 28 street lamps leaking down the street.

The answer process is as follows

1) There are a total of x street lights on this street.

2) According to each street lamp, 5 bulbs should be installed. A total of 140 light bulbs are needed for this street. The available equation is: spine 5x=140.

3) Solution: x=140 5=28.

20-1=19 (pcs), A: There are 19 billboards in total

So the answer is: 19

400 Here's why.

3000 30=100 The number of places where billboards are placed on one side.

100 * 2 = 200 put two in one place, multiply by 2 means that one regrets the shoot and put 200200 * 2 = 400 two mountains and mausoleums multiply 2

20-1=19 (pcs), A: There are 19 billboards in total

So the answer is: 19

Reckoning to put one between the two lamps.

Put two between the three.

Put three between the four.

The pattern comes out.

Between 100 lamps, put 100-1=99.