Final answer:
Using the midpoint method, the average of the initial and final price of umbrellas is calculated, resulting in a midpoint price of $110.
Step-by-step explanation:
When using the midpoint method to calculate the percentage change in price, you first identify the initial and final prices and then find the midpoint (average) of these two prices. Next, you calculate the change in price and divide it by the midpoint, multiplying by 100 to obtain the percentage change.
In this case, the initial price of an umbrella is $100, and the final price is $120. The midpoint (average) price is calculated by adding the initial and final prices and then dividing by 2:
Midpoint Price = (Initial Price + Final Price) / 2
Midpoint Price = ($100 + $120) / 2
Midpoint Price = $220 / 2
Midpoint Price = $110