In an NGO, the daily average wages of 20 illiterate employees decrease from Rs 25 to Rs 10. As a result, the average daily salary of all employees, including both literate and illiterate workers, decreases by Rs 10 per day. How many educated (literate) employees are working in the NGO?

Introduction:
This question involves a change in average wages caused by a reduction in the wages of a subgroup of employees. You are asked to determine the number of educated employees from the information about how the overall average changes.

Given Data / Assumptions:
Number of illiterate employees = 20. Their daily wage decreases from Rs 25 to Rs 10. The overall average wage of all employees decreases by Rs 10. Number of literate employees = let this be x. Assume literate employees wages remain unchanged.

Concept / Approach:
The key idea is that a change in the average of the entire group is caused by a change in the total sum of wages, while the total number of workers stays the same. We: 1. Calculate the total decrease in wages of the 20 illiterate workers. 2. Relate that to the decrease in average wage of all employees. 3. Use this to find the total number of employees and then the number of educated workers.

Step-by-Step Solution:
Step 1: Change in wage per illiterate employee = 25 - 10 = Rs 15. Step 2: Total decrease in wages for 20 illiterate employees = 20 * 15 = Rs 300 per day. Step 3: Let the total number of employees (literate + illiterate) be N. Due to the wage cut, the average salary of all employees decreases by Rs 10 per day. Step 4: Total decrease in wages for all employees = N * 10. But we know the only change is from the illiterate group, which is Rs 300. So, N * 10 = 300. N = 300 / 10 = 30. Step 5: We know there are 20 illiterate employees, so literate employees x = N - 20. x = 30 - 20 = 10.

Verification / Alternative Check:
If there are 30 employees, and their overall average falls by Rs 10, the total reduction must be Rs 300. This matches the reduction caused by the 20 illiterate employees: 20 * 15 = 300. Therefore, the logic and the numbers are consistent.

Why Other Options Are Wrong:
15 or 20: These values would give a different total N and would not produce a total reduction of exactly Rs 300 when multiplied by the decrease in the average. 25: This would imply too many employees, giving a total reduction far greater than Rs 300. Data insufficient: The data is sufficient because the change in average and the change in individual wages fully determine the total number of employees.

Common Pitfalls:
Some students try to set up two separate average equations involving actual wages of literate employees, which is unnecessary. Others forget that the change in average multiplied by the total number of workers equals the net change in total wages. Always convert average changes to total changes and then reason about counts.

Final Answer:
The number of educated employees working in the NGO is 10.