A vendor purchased bananas at Rs. 40 per dozen and sold them at 10 for Rs.36. Find his gain or loss per cent.

Answer

To solve the problem, we need to find the cost price (CP) and selling price (SP) of the bananas and then calculate the gain or loss percentage.

### Step-by-Step Solution:

1. **Determine the Cost Price (CP) of Bananas:**
- The vendor purchased bananas at Rs. 40 per dozen.
- Since 1 dozen = 12 bananas, the cost price per banana is:
\[ \text{CP per banana} = \frac{40}{12} = \frac{10}{3} \approx 3.33 \text{ Rs} \]

2. **Determine the Selling Price (SP) of Bananas:**
- The vendor sold 10 bananas for Rs. 36.
- Therefore, the selling price per banana is:
\[ \text{SP per banana} = \frac{36}{10} = 3.6 \text{ Rs} \]

3. **Calculate the Gain or Loss per Banana:**
- Gain or Loss = SP - CP
- Substituting the values, we get:
\[ \text{Gain} = 3.6 - 3.33 = 0.27 \text{ Rs} \]

4. **Calculate the Gain Percentage:**
- Gain Percentage is calculated using the formula:
\[ \text{Gain Percentage} = \left( \frac{\text{Gain}}{\text{CP}} \right) \times 100 \]
- Substituting the values, we have:
\[ \text{Gain Percentage} = \left( \frac{0.27}{3.33} \right) \times 100 \approx 8.1\% \]

### Final Answer:
The vendor has a gain of approximately **8.1%**.