Common Core State Standard: 8.EE.5 

Grade  8 
Subject  MATH 
Domain  Expressions & Equations 
Theme  Understand the connections between proportional relationships, lines, and linear equations 
Standard  Graph proportional relationships, interpreting the unit rate as the slope of the graph. Compare two different proportional relationships represented in different ways. For example, compare a distancetime graph to a distancetime equation to determine which of two moving objects has greater speed. 
Reference URL  http://www.corestandards.org/Math/Content/8/EE 