The simple interest on a sum at 3% p.a in 3 years is ₹315. What is the compound interest on the same sum at 4% p.a in 2 years, interest compounded yearly?

The simple interest on a sum at 3% p.a in 3 years is ₹315.

$$simple\ interest\ =\frac{principal\times rate\times time}{100}$$

$$315=\frac{principal\times3\times3}{100}$$

principal = 3500

compound interest on the same sum at 4% p.a in 2 years, interest compounded yearly.

compound interest = $$principal\left[\left(1+\frac{rate}{100}\right)^{time}-1\right]$$

= $$3500\left[\left(1+\frac{4}{100}\right)^2-1\right]$$