7. Suppose that a market has the demand function Qd = 20 - 0.5P. Using the midpoint method, what is the price elasticity of demand between $30 and $40?

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**Question 7:**

Suppose that a market has the demand function \( Q_d = 20 - 0.5P \). Using the midpoint method, what is the price elasticity of demand between $30 and $40?

---

**Explanation:**

To find the price elasticity of demand using the midpoint method, we use the following formula:

\[
\text{Price Elasticity of Demand (E_d)} = \frac{\left(\frac{Q_2 - Q_1}{(Q_2 + Q_1)/2}\right)}{\left(\frac{P_2 - P_1}{(P_2 + P_1)/2}\right)}
\]

Where:
- \(Q_1\) and \(Q_2\) are the quantities demanded at prices \(P_1\) and \(P_2\), respectively.
- \(P_1\) and \(P_2\) are the two different prices.

Given the demand function \( Q_d = 20 - 0.5P \):

1. Calculate \(Q_1\) when \(P_1 = 30\):
   \[
   Q_1 = 20 - 0.5 \times 30 = 5
   \]

2. Calculate \(Q_2\) when \(P_2 = 40\):
   \[
   Q_2 = 20 - 0.5 \times 40 = 0
   \]

3. Substitute the values into the midpoint formula to find \(E_d\):
   \[
   E_d = \frac{\left(\frac{0 - 5}{(0 + 5)/2}\right)}{\left(\frac{40 - 30}{(40 + 30)/2}\right)} = \frac{\left(\frac{-5}{2.5}\right)}{\left(\frac{10}{35}\right)}
   \]

   \[
   E_d = \frac{-2}{0.2857} \approx -7
   \]

The price elasticity of demand between $30 and $40 is approximately \(-7\), indicating that the demand is elastic in this price range.
Transcribed Image Text:**Question 7:** Suppose that a market has the demand function \( Q_d = 20 - 0.5P \). Using the midpoint method, what is the price elasticity of demand between $30 and $40? --- **Explanation:** To find the price elasticity of demand using the midpoint method, we use the following formula: \[ \text{Price Elasticity of Demand (E_d)} = \frac{\left(\frac{Q_2 - Q_1}{(Q_2 + Q_1)/2}\right)}{\left(\frac{P_2 - P_1}{(P_2 + P_1)/2}\right)} \] Where: - \(Q_1\) and \(Q_2\) are the quantities demanded at prices \(P_1\) and \(P_2\), respectively. - \(P_1\) and \(P_2\) are the two different prices. Given the demand function \( Q_d = 20 - 0.5P \): 1. Calculate \(Q_1\) when \(P_1 = 30\): \[ Q_1 = 20 - 0.5 \times 30 = 5 \] 2. Calculate \(Q_2\) when \(P_2 = 40\): \[ Q_2 = 20 - 0.5 \times 40 = 0 \] 3. Substitute the values into the midpoint formula to find \(E_d\): \[ E_d = \frac{\left(\frac{0 - 5}{(0 + 5)/2}\right)}{\left(\frac{40 - 30}{(40 + 30)/2}\right)} = \frac{\left(\frac{-5}{2.5}\right)}{\left(\frac{10}{35}\right)} \] \[ E_d = \frac{-2}{0.2857} \approx -7 \] The price elasticity of demand between $30 and $40 is approximately \(-7\), indicating that the demand is elastic in this price range.
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