The amount is increased by 40 in 4 years at simple interest What will be the compound interest of Rs...........

Explanation:

Let P = Rs.100
Simple Interest = Rs. 40
Rate of interest=(100×SI)/PT =(100×40)/(100×4)=10% per annum
Now, P = Rs.20,000
T = 2 years
R = 10%
Amount after 2 years =P(1+R/100)^t
=20000(1+10/100)^2
=20000(110/100)^2
=20000(11/10)^2 =24,200
Compound Interest = Rs.24,200 – Rs.20,000 = Rs.4,200

Hence, option 3 is the correct answer.