The formula provided in the image is:

$N = L - dL$

Where:

• $N$ represents the net price,
• $L$ is the list price,
• $dL$ is the amount of the discount.

From the image:

• The amount of the discount, $dL$, is $9.90,
• The net price, $N$, is $20.10.

Step 1: Solve for the list price $L$.

We know that: $N = L - dL$ Substitute the values: $20.10 = L - 9.90$ Solving for $L$: $L = 20.10 + 9.90 = 30.00$ So, the list price $L$ is $30.00.

Step 2: Calculate the discount rate.

The discount rate $d$ is calculated using: $d = \frac{dL}{L}$ Substitute the known values: $d = \frac{9.90}{30.00} = 0.33$ So, the discount rate is 33%.

Final Answer: The discount rate is 33%.

Would you like further details or clarification? Here are a few related questions to explore:

1. How would the discount rate change if the net price were different?
2. How do you calculate the amount of a discount from a given discount rate?
3. What happens to the net price if the list price is increased, keeping the discount rate constant?
4. How do you calculate the list price if you know the discount amount and the discount rate?
5. How can this formula be applied in real-world scenarios such as retail pricing?

Tip: When working with discounts, it’s helpful to first find the list price before calculating the discount rate, especially if the net price is given.