4. The demand for high top bell knots by the equation Q=50-2P

A. What is the point price elasticity of demand at p=20
B. if the price where to fall to 15 , what should happen to total expenditures on this product &wjat would this imply about the price elasticity of demand ?

1 answer

### Part A: Point Price Elasticity of Demand at \( P = 20 \)

The point price elasticity of demand (\(E_d\)) is given by the formula:

\[ E_d = \left( \frac{dQ}{dP} \right) \times \left( \frac{P}{Q} \right) \]

Given the demand equation \( Q = 50 - 2P \):

1. First, find the derivative of \( Q \) with respect to \( P \):
\[ \frac{dQ}{dP} = -2 \]

2. Next, find \( Q \) when \( P = 20 \):
\[ Q = 50 - 2(20) = 50 - 40 = 10 \]

3. Now, plug these values into the elasticity formula:
\[ E_d = (-2) \times \left( \frac{20}{10} \right) \]
\[ E_d = -2 \times 2 \]
\[ E_d = -4 \]

So, the point price elasticity of demand at \( P = 20 \) is -4.

### Part B: Effect on Total Expenditures when Price Falls to \( P = 15 \)

Total expenditures (or total revenue) can be found by multiplying price (\( P \)) by quantity (\( Q \)):
\[ \text{Total Expenditures} = P \times Q \]

Let's calculate the quantity demanded when the price falls to \( P = 15 \):
\[ Q = 50 - 2(15) = 50 - 30 = 20 \]

Now, calculate the total expenditures at \( P = 15 \):
\[ \text{Total Expenditures} = 15 \times 20 = 300 \]

Now, the total expenditures at the initial price \( P = 20 \):
\[ Q = 10 \]
\[ \text{Total Expenditures} = 20 \times 10 = 200 \]

Comparing the total expenditures:
- At \( P = 20 \), total expenditures are 200.
- At \( P = 15 \), total expenditures are 300.

Total expenditures have increased when the price falls from 20 to 15.

**Implication about Elasticity:**

Since total expenditures increase when the price decreases, this implies that the demand for high top bell knots is price elastic in this price range.

- When the elasticity \( |E_d| > 1 \), demand is elastic, and a decrease in price leads to an increase in total revenue.
- Conversely, when the elasticity \( |E_d| < 1 \), demand is inelastic, and a decrease in price would lead to a decrease in total revenue.

With an elasticity of -4 at \( P = 20 \), the demand is highly elastic. This matches our observation that reducing the price to \( P = 15 \) increases total revenue, confirming that demand in this price range is indeed elastic.