Mukund invests a sum of Rs. 5400 and Sachin invests a sum of Rs. 9400 at the same rate of simple interest per annum. If, at the end of 4 years, Sachin gets Rs. 960 more interest than Mukund, then find the rate of interest per annum (in percentage).

Correct option is C

Given:
​Principal of Mukund (P₁) = Rs. 5400
​Principal of Sachin (P₂) = Rs. 9400
​Time (T) = 4 years
​Difference in Interest = Rs. 960
​Formula Used:
​Simple Interest (SI) = (P × R × T) / 100
​Solution:
​Let the rate of interest be R%.
​Interest by Sachin - Interest by Mukund = Rs. 960
​​$$\Rightarrow \frac{9400 \times R \times 4}{100} - \frac{5400 \times R \times 4}{100} = 960\\\Rightarrow \left( \frac{R \times 4}{100} \right) \times (9400 - 5400) = 960\\\Rightarrow \left( \frac{R \times 4}{100} \right) \times 4000 = 960\\\Rightarrow \frac{R \times 16000}{100} = 960\\\Rightarrow 160R = 960\\\Rightarrow R = \frac{960}{160} = 6\%$$​​​
​Therefore, the rate of interest per annum is 6%.​