Explanation:

- Purchase Details:

- 40 chairs are bought at the price of 36 chairs.

- This means, for every 36 chairs, the cost covers 40 chairs.

- The cost per chair in terms of purchase is effectively reduced.

- Understanding the Marked Price and Purchase Price:

- Let the marked price of each chair be 'x'.

- Total marked price for 40 chairs = 40x.

- Amount paid = 36x (since 40 chairs bought at price of 36 chairs).

- Selling Details:

- A 1% discount is given on the marked price.

- Selling price per chair after 1% discount = 0.99x.

- Total selling price for 40 chairs = 40 * 0.99x = 39.6x.

- Profit Calculation:

- Cost Price (CP) for 40 chairs = 36x.

- Selling Price (SP) for 40 chairs = 39.6x.

- Profit = SP - CP = 39.6x - 36x = 3.6x.

- Profit Percentage = (Profit / CP) * 100 = (3.6x / 36x) * 100 = 10%.

- Correct Option:

- The correct answer is Option: 4, 10%.