Welcome to our Math lesson on Graph of Direct Proportion, this is the third lesson of our suite of math lessons covering the topic of Proportion, you can find links to the other lessons within this tutorial and access additional Math learning resources below this lesson.
In ratio tutorial 4.1 we proved that ratios produce a linear graph. Since the direct proportion is obtained by two equal ratios, it is easy to conclude that the graph representing a direct proportion is a straight (sloped) line that starts from the origin (otherwise it is not a direct proportion), where the slope is determined by the simplest form of the ratio or of the unit rate.
Let's consider one such a graph to clarify this point.
The graph below is not an example of direct proportion because the ratios of position at the two given instants are not the same as the ratios of time. In other words, 320/110 is different from 20/10, as the first ratio gives 1.5 and the second gives 2.
Therefore, the quantities involved in the above situation are not directly proportional. In simpler words, the graph must start from the origin in order to have a direct proportion, as shown below.
Here, both ratios are the same as 220/110= 20/10 = 2. Therefore, the quantities involved are directly proportional (or simply, proportional).
Remark! It is better to solve the situations with ratios, not with rates when dealing with proportions. In other words, it is better to divide two like quantities instead of the unlike ones.
Which of the following situations involves a direct proportion?
|Tutorial ID||Math Tutorial Title||Tutorial||Video|
|Lesson ID||Math Lesson Title||Lesson||Video|
|4.3.1||Definition of Proportion|
|4.3.3||Graph of Direct Proportion|
|4.3.4||Cross Product in Direct Proportion|
|4.3.5||Inverse (Indirect) Proportion|
|4.3.6||Graph of Inverse Proportion|
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