Common Core State Standard: 7.EE.4 

Grade  7 
Subject  MATH 
Domain  Expressions & Equations 
Theme  Solve reallife and mathematical problems using numerical and algebraic expressions and equations 
Standard  Use variables to represent quantities in a realworld or mathematical problem, and construct simple equations and inequalities to solve problems by reasoning about the quantities. 
Reference URL  http://www.corestandards.org/Math/Content/7/EE 