To calculate the percentage decrease in the stock price, use the formula:

$\text{Percentage Decrease} = \frac{\text{Original Price} - \text{New Price}}{\text{Original Price}} \times 100$

Step 1: Plug in the values

The original price is $15$, and the new price is $9$:

$\text{Percentage Decrease} = \frac{15 - 9}{15} \times 100$

Step 2: Perform the calculations

1. Subtract $9$ from $15$: $15 - 9 = 6$
2. Divide $6$ by $15$: $\frac{6}{15} = 0.4$
3. Multiply $0.4$ by $100$: $0.4 \times 100 = 40$

Final Answer:

The percentage decrease is 40.

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Would you like additional details or explanations? Here are 5 related questions:

1. How can percentage decrease be applied to financial forecasting?
2. What is the difference between percentage decrease and percentage change?
3. How do you calculate the percentage increase instead of decrease?
4. If the stock price drops further to $6, what would the new percentage decrease be?
5. How can businesses use percentage decrease to analyze stock performance?

Tip: Always double-check calculations for accuracy, especially when rounding percentages!