Find the simple interest on Rs 3000 invested at 18% per annum for a period of 73 days, assuming a 365-day year and simple interest throughout, and express the interest in rupees correct to the nearest rupee.

Introduction / Context:
This question involves calculating simple interest for a fractional part of a year. Instead of time being given in whole years, it is provided in days, and you are told to assume a 365-day year. Such problems are common in banking and finance aptitude tests because they reflect how interest is often computed for short-term investments or loans.

Given Data / Assumptions:

Principal P = Rs 3000.
Rate of interest R = 18% per annum.
Time T = 73 days, with a 365-day year assumption.
Simple interest formula: SI = (P * R * T) / 100, where T is in years.
We must convert 73 days into its equivalent in years using 365 days per year.

Concept / Approach:
The key idea is to express the time in years before substituting into the simple interest formula. Once T is expressed as 73 / 365 years, we plug P, R, and T into SI = (P * R * T) / 100. After computing, we round the result to the nearest whole rupee, as the options are given in rupees without paise.

Step-by-Step Solution:
Step 1: Convert days to years. T = 73 days = 73 / 365 years. Step 2: Write the simple interest formula: SI = (P * R * T) / 100. Step 3: Substitute P = 3000, R = 18, T = 73 / 365. Step 4: SI = (3000 * 18 * 73 / 365) / 100. Step 5: Simplify the expression: 73 / 365 = 1 / 5. So SI = (3000 * 18 * 1 / 5) / 100. Step 6: Compute 3000 * 18 = 54000. Step 7: Then 54000 * (1 / 5) = 10800. Step 8: Finally, divide by 100: SI = 10800 / 100 = 108. Step 9: Therefore, the simple interest is Rs 108.

Verification / Alternative check:
Another way to see this is to first compute the annual interest and then scale by the fraction of the year. Annual interest at 18% on Rs 3000 is 3000 * 18 / 100 = 540. For 73 days out of 365, interest = 540 * 73 / 365. Since 73 / 365 = 1 / 5, we get 540 * 1 / 5 = 108, consistent with the detailed calculation.

Why Other Options Are Wrong:
Values such as Rs 118, Rs 105, Rs 110, and Rs 112 result from incorrect handling of the fraction of the year, using 360 days instead of 365 days, or rounding at intermediate steps. Only Rs 108 exactly matches the correct computation based on a 365-day year and the given rate.

Common Pitfalls:
Common mistakes include treating 73 as 73 months, using 12 months or 360 days incorrectly, or forgetting to divide by 100 after multiplying P, R, and T. Another error is rounding too early, rather than after completing the full calculation. Always convert days to years carefully and perform the operations in the correct order.

Final Answer:
The simple interest on the investment is Rs 108.