A sum of money invested at simple interest becomes $$\frac{13}{10}$$ of itself in 2 years and 6 months. What is the rate (in percentage) of interest per annum?
Let sum of money invested = Rs. $$100x$$
=> Amount under simple interest = $$\frac{13}{10}\times100x=Rs.$$ $$130x$$
Thus, simple interest = $$130x-100x=Rs.$$ $$30x$$
Let rate of interest = $$r\%$$ and time period = 2.5 years
=> Simple interest = $$\frac{P\times R\times T}{100}$$
=> $$\frac{100x\times r\times2.5}{100}=30x$$
=> $$2.5r=30$$
=> $$r=\frac{30}{2.5}=12\%$$
=> Ans - (C)
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