In a dairy farm, 40 cows eat 40 bags of husk in 40 days. Assuming the rate of eating is constant and the cows are identical in consumption, in how many days will one cow eat one bag of husk?

Introduction / Context:
This is a standard work-rate style question framed in terms of cows and husk consumption. It tests your understanding of unit consumption (one cow-day) and how to convert total consumption across many animals and days into the rate for a single animal and a single bag.

Given Data / Assumptions:
- 40 cows eat 40 bags of husk in 40 days.
- All cows eat at the same constant rate.
- We need the number of days in which one cow will eat one bag of husk.

Concept / Approach:
We treat consumption in cow-days and bag-units. Total consumption in the given scenario is 40 bags. We express this consumption as cow-days and then find how many cow-days are needed per bag. Finally, we convert cow-days per bag into days for one cow per bag.

Step-by-Step Solution:
Step 1: Compute total cow-days: 40 cows * 40 days = 1600 cow-days.Step 2: During these 1600 cow-days, the cows consume 40 bags of husk.Step 3: So cow-days per bag = 1600 cow-days / 40 bags = 40 cow-days per bag.Step 4: This means that one bag of husk requires 40 cow-days of eating.Step 5: If we have just one cow, each day contributes 1 cow-day.Step 6: Therefore, to reach 40 cow-days with one cow, we need 40 days.

Verification / Alternative check:
Consider the daily total consumption: 40 bags in 40 days means 1 bag per day by all 40 cows together. Thus, per cow per day, the consumption is 1/40 bag. To eat 1 bag at this rate, one cow needs time = 1 / (1/40) = 40 days, confirming the earlier calculation.

Why Other Options Are Wrong:
1 day would mean all 40 cows together eat 40 bags per day, contradicting the data. 1/40 day is an extreme misinterpretation of the rate. 20 or 80 days do not match the cow-day calculation and arise from mistakes such as halving or doubling the result without reason. Only 40 days preserves the correct proportional consumption.

Common Pitfalls:
Students sometimes assume that if 40 cows eat 40 bags in 40 days, then one cow eats one bag in 1 day, incorrectly ignoring the time dimension in the original statement. Others miscalculate cow-days per bag. Always convert to a per cow per day rate or use cow-days systematically to avoid confusion.

Final Answer:
One cow will eat one bag of husk in 40 days.