Introduction:
In order to determine the marginal revenue of an increase in output from 9 to 10 units, we need to understand the concept of marginal revenue and how it is calculated.

Understanding Marginal Revenue:
Marginal revenue refers to the additional revenue generated from selling one more unit of a product or service. It is calculated by dividing the change in total revenue by the change in quantity sold.

Given Information:
- Price at 9 units: Rs 20
- Quantity demand at 9 units: 9 units
- Price at 10 units: Rs 19
- Quantity demand at 10 units: 10 units

Calculating Marginal Revenue:
To calculate the marginal revenue of an increase in output from 9 to 10 units, we need to find the change in total revenue and the change in quantity sold.

Change in Total Revenue:
The change in total revenue can be calculated by subtracting the total revenue at 9 units from the total revenue at 10 units.

Total revenue at 9 units = Price at 9 units * Quantity demand at 9 units
= Rs 20 * 9
= Rs 180

Total revenue at 10 units = Price at 10 units * Quantity demand at 10 units
= Rs 19 * 10
= Rs 190

Change in total revenue = Total revenue at 10 units - Total revenue at 9 units
= Rs 190 - Rs 180
= Rs 10

Change in Quantity Sold:
The change in quantity sold can be calculated by subtracting the quantity demand at 9 units from the quantity demand at 10 units.

Change in quantity sold = Quantity demand at 10 units - Quantity demand at 9 units
= 10 units - 9 units
= 1 unit

Final Calculation:
Now, we can calculate the marginal revenue by dividing the change in total revenue by the change in quantity sold.

Marginal revenue = Change in total revenue / Change in quantity sold
= Rs 10 / 1
= Rs 10

Conclusion:
Therefore, the marginal revenue of an increase in output from 9 to 10 units is Rs 10. This means that by producing and selling one additional unit, the company generates an additional revenue of Rs 10.

10 rupees