Find the simple interest on Rs. 600 for 11 months if the rate of interest is 5 paise per rupee per month (equivalently 5% per month).

Introduction / Context:
This problem involves simple interest with a rate given per month per rupee instead of per year. You need to interpret “5 paise per rupee per month” correctly and then compute the simple interest for 11 months on a principal of Rs. 600.

Given Data / Assumptions:

• Principal (P) = Rs. 600.
• Time = 11 months.
• Rate = 5 paise per rupee per month, which is equivalent to 5% per month.
• Simple interest is used, not compound interest.

Concept / Approach:
One rupee is 100 paise, so 5 paise per rupee is 5 out of 100, which is 0.05 rupee per rupee per month, or 5% per month. You can either treat the rate as a monthly rate and apply SI = P * r * t, with r as 5% per month and t in months, or convert it to an annual rate of 60% per annum and treat the time as 11/12 of a year.

Step-by-Step Solution:
Step 1: Interpret the rate: 5 paise per rupee per month means 5% per month. Step 2: Use the simple monthly interest formula: SI = P * r * t, where r is the rate per month in decimal form. Step 3: Here P = 600, r = 5% per month = 0.05, time t = 11 months. Step 4: Compute SI = 600 * 0.05 * 11. Step 5: First 600 * 0.05 = 30. Step 6: Then 30 * 11 = Rs. 330.

Verification / Alternative check:
Alternatively, convert the monthly rate to an annual rate: 5% per month over 12 months gives 5 * 12 = 60% per annum. The time is 11 months, which is 11 / 12 of a year. Using SI = (P * R * T) / 100 with R = 60 and T = 11 / 12 also gives SI = (600 * 60 * 11 / 12) / 100 = 330, confirming the answer.

Why Other Options Are Wrong:
Rs. 30 and Rs. 3.30 are far too small and arise from misinterpreting the rate as annual instead of monthly. Rs. 33 is also too small and likely comes from taking a single month of interest only instead of 11 months.

Common Pitfalls:
The most frequent mistake is to assume the given rate is per year or to misread 5 paise per rupee per month as 5 paise per month in total. It is critical to notice that the rate is per rupee and per month, which significantly increases the effective annual rate. Correct unit handling is essential in such problems.

Final Answer:
The simple interest on Rs. 600 for 11 months at this rate is Rs. 330.