Final answer:
The original sum invested, using the compound interest formula with rates of 5%, 10%, and 20% for three consecutive years and amounting to Rs 1386, is Rs 1000. Therefore, the correct option is D.
Step-by-step explanation:
The question involves finding the original sum invested after applying compound interest rates over three different years. To solve this, we will use the formula for compound interest, which incorporates the principal amount, the interest rate, and the number of time periods the interest is applied for.
Let's denote the principal amount as 'P' and use the given compound interest rates 5%, 10%, and 20% for the first, second, and third year respectively.
We calculate the future value using the formula:
P(1+0.05)(1+0.10)(1+0.20) = 1386
We simplify this equation to find the value of P.
Assuming correct calculations, P = Rs 1000, which means that Rs 1000 is the original sum invested, and after three years with the given compounded rates, it amounts to Rs 1386.