Answer:
- Change in quantity demanded: Represent a change of total demands of a product that is caused by the price of the product.
When the price of a product increased, the amount of consumers who can afford to buy that product is decreased, As a result, this cause a decrease in overall demand over that product. (The opposite happened when the price of product is decreased)
- a shift in the demand curve. : Represent a change of total demands of a product that is caused by other factors beside the price of the products.
Price is not the only one that can affect demands. For example, natural disaster could occurred and make a certain type of product become really scarce. This tend to lead to an increase of demand even if the price of that product remain the same.