₹ 1000 is invested at 5\% per annum simple interest. If the interest is added to the principal after every 10 years, the amount will become ₹ 2000 after
(a)15 years
(b)$16 \frac{2}{3}$ years
(c)18 years
(d)20 years
Answer
No answer key was printed for this question.
Explanation
Amount after 10 years $=₹\left[1000+\frac{1000 \times 5 \times 10}{100}\right]=₹ 1500$. Now, S.I. $=₹(2000-1500)=₹ 500, P=₹ 1500, R=5 \%$. $$\text { ∴ Time }=\left(\frac{500 \times 100}{1500 \times 5}\right) \mathrm{yrs}=6 \frac{2}{3} \mathrm{yrs} .$$ Hence, required time $=\left(10+6 \frac{2}{3}\right) \mathrm{yrs}=16 \frac{2}{3} \mathrm{yrs}$.
Explanation as extracted from the printed page; notation may be imperfect.