A borrowed रु 2,500 from B at 12% per annum compound interest. After 2 years, A gave रु 2,936 and a watch to B to clear the account. Find the cost of the watch.

Explanation

To solve the problem step by step, we will calculate the total amount A needs to pay back after 2 years using the compound interest formula and then find the cost of the watch.

### Step 1: Identify the given values
- Principal (P) = रु 2,500
- Rate of interest (R) = 12% per annum
- Time (T) = 2 years

### Step 2: Calculate the amount after 2 years using the compound interest formula
The formula for compound interest is:
\[ A = P \left(1 + \frac{R}{100}\right)^T \]
Substituting the values into the formula:
\[ A = 2500 \left(1 + \frac{12}{100}\right)^2 \]
\[ A = 2500 \left(1 + 0.12\right)^2 \]
\[ A = 2500 \left(1.12\right)^2 \]
\[ A = 2500 \times 1.2544 \quad (\text{since } 1.12^2 = 1.2544) \]
\[ A = 3136 \]

### Step 3: Calculate the cost of the watch
A paid a total of रु 2,936 and a watch to clear the account. Therefore, we need to find the cost of the watch:
\[ \text{Cost of the watch} = A - \text{Amount paid in cash} \]
\[ \text{Cost of the watch} = 3136 - 2936 \]
\[ \text{Cost of the watch} = 200 \]

### Final Answer
The cost of the watch is रु 200.

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