Q.What annual rate of simple interest will make the interest on a sum over 10 years equal to \(\cfrac{2}{5}\) of the total amount? (a) \(6\frac{1}{3}\%\) (b) \(6\%\) (c) \(6\frac{2}{3}\%\) (d) \(2\frac{1}{6}\%\)
Answer: C
Let the total amount \(= x\) taka \(\therefore\) Total interest \((I) = \cfrac{2x}{5}\) taka Principal \((P) = x - \cfrac{2x}{5} = \cfrac{3x}{5}\) taka Time \((t) = 10\) years \(\therefore\) Rate of interest \((r) = \cfrac{100 \times I}{P \times t}\%\) \(= \cfrac{100 \times \cfrac{2x}{5}}{\cfrac{3x}{5} \times 10}\%\) \(= \cfrac{100 \times 2x}{3x \times 10}\% = 6\frac{2}{3}\%\)
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