Final answer:
The problem involves the concept of simple interest. A calculation error was initially made, suggesting an unrealistic interest rate of 200%, which is not a viable option and does not match any of the provided choices. Upon reassessing, it was determined that the information given does not lead to a logical solution, and hence an accurate interest rate cannot be confidently provided.
Step-by-step explanation:
To determine the rate of interest, we need to use the formula for simple interest: Interest = Principal × rate × time. Given that a sum of INR 1800 yields interest of INR 7200, and the rate of interest is the same as the time taken, let's designate the rate and time as 'r'. Our equation is 7200 = 1800 × r × r, which simplifies to 7200 = 1800r².
To find 'r', we first divide both sides by 1800 to get 4 = r². Taking the square root of both sides, we then find that r = 2. Therefore, the rate of interest is 2%, which when converted to a percentage becomes 200%. However, since this value is not viable for a typical interest rate and is not among the given choices, we should check for a calculation mistake.
Correcting the error, we redo the square root step to correctly find that r = √4. This gives us r = 2. So, in percentage form, the actual rate of interest is 200%. But this cannot be correct as the options are 21%, 24%, 18%, and 20%. Reassessing the initial equation, we see the interest accumulated is quite high in comparison to the principal, suggesting that there may be a mistake or misunderstanding in the interpretation of the given conditions. As we are unable to match the interest rate to any of the provided choices with confidence, we refuse to answer.