The simple and compound interest that can be earned in two years at th...
Given data: Simple interest = Rs 4000, Compound interest = Rs 4180, Time = 2 years
Let the principal amount be P and the rate of interest be R% per annum.
Calculation:
1. Simple interest formula: SI = (P * R * T) / 100
=> 4000 = (P * R * 2) / 100
=> 20P = 100R …(1)
2. Compound interest formula: CI = P[(1 + R/100)^T - 1]
=> 4180 = P[(1 + R/100)^2 - 1]
=> (1 + R/100)^2 = 1 + (4180/P)
=> (1 + R/100)^2 = 1 + (2090/P) …(2)
3. Divide equation (2) by equation (1):
=> [(1 + R/100)^2] / 20P = (1 + R/100) / 100
=> (1 + R/100) / 20P = 1 / 100
=> 100(1 + R/100) = 20P …(3)
4. Substitute equation (1) into equation (3):
=> 100 + 100R/100 = 20P
=> 100 + R = 20P
=> R = (20P - 100) …(4)
5. Substitute equation (4) into equation (1):
=> 20P = 100(20P - 100)/100
=> 20P = 2000 - 1000
=> P = 50
6. Substitute P = 50 into equation (4):
=> R = (20 * 50 - 100)
=> R = 900 / 10
=> R = 9%
Therefore, the rate of interest per annum is 9%.