A total sum of Rs. 2000 money is invested at simple interest with interest rate 3%. The same amount is invested at double the rate of simple interest for one year compounded annually. What is the minimum time in which amount with simple interest becomes equal to the amount of the compound interest?

The simple interest amount after t years is 2000 plus 60t, using the 3% rate. The compound interest amount at the doubled rate of 6% after t years is 2000 multiplied by 1.06 to the power of t. Testing the options, when t is 2 years the simple interest amount is 2000 plus 120, which equals Rs. 2120, and the compound interest amount is 2000 times 1.06 squared, which also equals Rs. 2120. Therefore, the minimum time is 2 years.

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