Gopal invests a sum of Rs. 5400 and Akshay invests a sum of Rs. 10200 at the same rate of simple interest per annum. If, at the end of 4 years, Akshay gets Rs. 720 more interest than Gopal, then find the rate of interest per annum (in percentage).

Correct option is A

Given:
Gopal's investment = Rs. 5400
Akshay's investment = Rs. 10200
Time period for both = 4 years
The difference in interest = Rs. 720
Formula Used:
​$$\text{Simple Interest (SI)} = \frac{P \times R \times T}{100}$$​​
where,
P = Principal,
R = Rate of interest,
T = Time in years.
Solution:
Let the rate of interest per annum be R%.
Interest for Gopal = $$\frac{5400 \times R \times 4}{100} = \frac{21600 \times R}{100} = 216R$$​​

Interest for Akshay = $$\frac{10200 \times R \times 4}{100} = \frac{40800 \times R}{100} = 408R$$​​
The difference in interest = Interest for Akshay - Interest for Gopal
408R - 216R = 720
192R = 720
R = $$\frac{720}{192}$$​ = 3.75
Thus, the rate of interest per annum is 3.75%.