SI=P×r×t/100
=p×4×2/109=80
=1000

Principle=1000

Ci= p[1+r/100]^t
ci= 1000×104/100×104/100
= 1081.6 amount

Calculating Compound Interest
To calculate the compound interest on a certain sum for the same period, we need to consider the formula for compound interest:

Compound Interest (CI) = P(1 + r/n)^(nt) - P
Where:
- P is the principal amount
- r is the rate of interest
- n is the number of times interest is compounded per year
- t is the time the money is invested for
Let's calculate the principal amount using the given information about simple interest:
- Simple Interest (SI) = 80
- Rate of interest (r) = 4% = 0.04
- Time (t) = 2 years

Calculating Principal Amount
To calculate the principal amount, we use the formula for simple interest:

SI = (P * r * t)
80 = P * 0.04 * 2
Solving for P:
P = 80 / (0.04 * 2)
P = 80 / 0.08
P = 1000
Therefore, the principal amount is Rs 1000.

Calculating Compound Interest
Now, let's calculate the compound interest on the principal amount of Rs 1000 for 2 years at 4% interest rate:
CI = 1000 * (1 + 0.04/1)^(1*2) - 1000
CI = 1000 * (1.04)^2 - 1000
CI = 1000 * 1.0816 - 1000
CI = 1081.6 - 1000
CI = Rs 81.6
Therefore, the compound interest on the principal amount of Rs 1000 for 2 years at 4% interest rate is Rs 81.6.