If compound interest received on a certain amount in the 3rd year is Rs 12 100 what will be the comp...........

Quantitative Aptitude (CGL) Compound Interest

If compound interest received on a certain amount in the 3rd year is Rs. 12,100, what will be the compound interest (in Rs) for the 4th year on the same amount if rate of interest is 9%?

17080

15669

13189

14376

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Explanation:

Let the principal be rs 100
Amount after 3 years=p (1+9/100)^3
=100 (1.09)^3
=129.5029————’(1)
Amount after 2 years=100 (1.09)^2
=rs.118.81—————(2)
Interest for 3rd year=(1)-(2)
129.5029-118.81= rs.10.6929
For 3rd year interest rs10.6929 principal is 100
So for rs 12100 interest; principal=12100×100/10.6929=113159.199 approx.
Note it assumed that use of calculator is allowed if not it is to be solved with the help of logaritham tables.
Now we calculet amount after 3 years and 4 years
A=113159 (1+9/100)^3
=113159 (1.09)^3=113159×1.295029———(4)
A=113159 (1.09)^4=113159 (1.411581)——-(5)
(5)-(4) is the interest for 4th year
113159 (1.411581-1.295029)=113159×0.116522
=13189