What is the compound interest on a sum of ₹7200 for $$2\frac{2}{5}$$ years at 20% p.a., interest compounded yearly (nearest to an integer)?

Principle(p) = 7200
Time(t) = $$2\frac{2}{5}$$ years = 2 + 2/5 years
r = 20%
Compound interest for 2 years = p(1 + $$\frac{r}{100})^2 - p$$
= 7200(1 + $$\frac{20}{100})^2 - 7200$$ = 7200($$\frac{6}{5})^2 - 7200$$
= 7200 $$\times \frac{36}{25} - 7200$$ = 10368 - 7200 = Rs.3168
Now,
p1 = Rs.10368
Compound interest for 2/5 years = $$\frac{prt}{100}$$
= $$\frac{10368 \times 20 \times 2}{100 \times 5}$$ = 829.44
Total interest = 3168 + 829.44 = Rs.3997.44