The graph of a proportionaly should always show data points on a perfect straight line that goes through the origin of coordinate (0, 0). because they relate to each other via a relationship like:
[tex]\frac{y}{x}=k[/tex]
That is: the ratio of the quantity y over x is a constant number "k".
Since you have this happening, then solving for one of the quantities (let say y)
we get:
y = k x
Now notice that the graph this person plotted consists of TWO lines, SO is such assumption correct?
