A certain sum invested at 10% per annum compound interest compounded half yearly, amounts to Rs.551.25 at the end of one year. The sum is:

500

Given rate = 10%

Time = 1 year

( The interest is compounded half yearly then, )

Effective rate will be = 5 + 5 + \(\frac{5 × 5}{100}\) = 10.25%

Amount = Principle + interest = 100% + 10.25% = 110.25%

110.25% = 551.25 

100% = 500(Sum)