correct answer is: b) ₹3200

Explanation

Here,
Amount(A) KaTeX parse error: KaTeX doesn't work in quirks mode.
Rate(R) KaTeX parse error: KaTeX doesn't work in quirks mode.% or KaTeX parse error: KaTeX doesn't work in quirks mode.%
Time(T) KaTeX parse error: KaTeX doesn't work in quirks mode. years
Principal(P) KaTeX parse error: KaTeX doesn't work in quirks mode. _{[the sum]}
We know, S.I. KaTeX parse error: KaTeX doesn't work in quirks mode.
According to the question,
Amount KaTeX parse error: KaTeX doesn't work in quirks mode. (Principal KaTeX parse error: KaTeX doesn't work in quirks mode. S.I.)
KaTeX parse error: KaTeX doesn't work in quirks mode. Amount KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode. _{[cross multiply]}
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode.
KaTeX parse error: KaTeX doesn't work in quirks mode. The sum is KaTeX parse error: KaTeX doesn't work in quirks mode.
Ans: The sum is KaTeX parse error: KaTeX doesn't work in quirks mode.

These precise math questions can also be expressed as:

1. How to calculate the initial sum when it grows to ₹3920 over 3 years at an annual interest rate of 7 ½%?
2. What is the principal amount needed to achieve a total of ₹3920 after 3 years with an annual interest rate of 7 ½%?
3. How to find the principal amount when the interest rate is 7 ½% per annum and the total amount is ₹3920 after 3 years?
4. Finding the principal sum required to yield ₹3920 in 3 years at an interest rate of 7 ½% per annum.