Increase; increase
being a perfect substitute for tea when the price of coffee increases the market price also increases and the market quantity of tea also increases as it is relatively cheaper than coffee.
Substitute Goods:
A substitute good can also be a service rather than just a tangible item. It is actually defined as a good or service that replaces another. For instance, more customers may choose to go to Burger King or KFC when the price of McDonald's rises. A similar product that can be used in place of another is what is meant by a substitute good, to put it another way. In other words, it resembles it enough to serve the same purpose. For instance, since both the iPhone and the Galaxy Note function as mobile phones, they both serve as substitutes
Substitute goods ensure there is a competitive environment. This is important because it helps keep prices down, and quality up.
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