what is  the need of substitute goods?

​​​​​​DEAR STUDENT, Substitute goods are those goods whose demand of the given good and price of the other good are directly proportional.for example tea and coffee.. substitute goods are those goods which can be used instead of the other... if we go to a restaurant and find price of coffee more than that of tea, a general tendency of the consumer will be to switch over to tea from that of coffee... so here we see that when price of coffee increases demand for coffee decreases as a result demand for nits substitute good ie tea increase . thus price of the given good and demand of the other good is directly proportional in case of substitute goods. REGARDS.