Let principal amount = Rs. $$100x$$ => Simple interest = $$frac{5}{100} imes100x=Rs.$$ $$5x$$ Let rate of interest = $$r\%$$ and time period = 10 years => Simple interest = $$frac{P imes R imes T}{100}$$ => $$frac{100x imes r imes10}{100}=5x$$ => $$10r=5$$ => $$r=frac{5}{10}=0.5\%$$ Let the interest will be equal to the principal in = $$t$$ years at 0.5% rate => $$frac{100x imes 0.5 imes t}{100}=100x$$ => $$t=frac{100}{0.5}=200$$ years => Ans - (C)