To solve this problem, we need to understand the relationship between the number of laborers and the time it takes to build the wall. We are given that 25 laborers can build the wall in 4 days. This means that if we decrease the number of laborers, the time required to build the wall will increase.



To find out how long it will take for 20 laborers to build the wall, we can use the concept of man-days. A man-day is the amount of work done by one laborer in one day.

We are given that 25 laborers can complete the wall in 4 days, which means that the total number of man-days required to build the wall is 25 x 4 = 100 man-days.

Now, let's calculate the number of man-days required when only 20 laborers are available.



To calculate the number of man-days, we use the formula:
Number of man-days = Number of laborers x Number of days

Given that there are 20 laborers and we need to find the number of days, we can rearrange the formula as follows:
Number of days = Number of man-days / Number of laborers

Substituting the values, we get:
Number of days = 100 man-days / 20 laborers = 5 days

Therefore, if only 20 laborers report for work, it will take them 5 days to build the wall.



In conclusion, we can determine the time required to build a wall by considering the number of laborers and the concept of man-days. By using the given information that 25 laborers can build the wall in 4 days, we can calculate that if only 20 laborers are available, it will take 5 days to complete the wall.

5 days