If a certain sum of money doubles itself in 7 years 8 months at simple interest, then what will be the yearly rate of interest (in %)?
Let the sum of money = Rs. $$x$$
=> Interest after 7years 8 months = Rs. $$(2x-x)=Rs.$$ $$x$$
Time period = 7 years 8 months = $$7\frac{8}{12}=\frac{23}{3}$$ years
Let rate of interest = $$r\%$$
=> Simple interest = $$\frac{P\times r\times t}{100}$$
=> $$\frac{x\times r\times\frac{23}{3}}{100}=x$$
=> $$23r=300$$
=> $$r=\frac{300}{23}=13\frac{1}{23}\%$$
=> Ans - (B)
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