A sum of Rs. 15,000 is invested partly at 12% per annum and the remaining at 10% per annum simple interest. If the total interest at the end of 2 years is Rs. 3,344, then how much money was invested at 10% per annum?

The problem uses a weighted average method, but verifying the given options is necessary because the provided total interest of Rs. 3,344 contradicts standard calculations. Testing the correct result of Rs. 6,400 at 10% yields an interest of Rs. 1,280 over two years, leaving Rs. 8,600 at 12% to generate Rs. 2,064 in interest. Adding these interests gives a total of Rs. 3,344, so the amount invested at 10% is Rs. 6,400.

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