Whenever we have a situation involving [b]constant rates[/b], we are likely to have a proportional relationship between quantities of interest.[br][br][list][*]When a bird is flying at a [b]constant speed[/b], then there is a proportional relationship between the flying time and distance flown.[/*][/list][list][*]If water is filling a tub at a [b]constant rate[/b], then there is a proportional relationship between the amount of water in the tub and the time the tub has been filling up.[/*][/list][list][*]If an aardvark is eating termites at a [b]constant rate[/b], then there is proportional relationship between the number of termites the aardvark has eaten and the time since it started eating.[/*][/list][br]Sometimes we are presented with a situation, and it is not so clear whether a proportional relationship is a good model. How can we decide if a proportional relationship is a good representation of a particular situation?[list][*]If you aren’t sure where to start, [b]look at the quotients of corresponding values[/b]. If they are not always the same, then the relationship is definitely not a proportional relationship.[/*][/list][list][*]If you can see that there is a single value that we always multiply one quantity by to get the other quantity, it is definitely a proportional relationship.[/*][/list][br]After establishing that it is a proportional relationship, setting up an equation is often the most efficient way to solve problems related to the situation.