A sum of money amounts to Rs. 9800 after 5 years and Rs. 12005 after 8 years at the same rate of simple interest. The rate of interest per annum is:
5%
8%
12%
15%
Explanation:
S.I. for 3 years = Rs. $\left(12005 - 9800\right)$ = Rs. 2205.
S.I. for 5 years = Rs.$ \left(\dfrac{2205}{3} \times 5\right) $= Rs. 3675
$\therefore$ Principal = Rs. $\left(9800 - 3675\right)$ = Rs. 6125.
Hence, rate =$ \left(\dfrac{100 \times 3675}{6125 \times 5} \right) $%= 12%