The compound interest calculated yearly at 10% on a certain sum of money amounts to रु 665.50 in the fifth year. Calculate :
(i) C.I. for the sixth year at the same rate and on the same sum.
(ii) C.I. for the fourth year on the same sum and at the same rate.

Explanation

To solve the problem step by step, we will calculate the compound interest for the sixth year and the fourth year based on the information provided.

### Given:
- Rate of interest (r) = 10%
- Compound interest for the fifth year (C.I. for the 5th year) = रु 665.50

### Step 1: Calculate the amount at the end of the fifth year (A5)
The formula for the amount at the end of n years with compound interest is:
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