How numbers help students solve physics problems
  Previous research has found that introductory physics students perform far better on numeric problems than on otherwise equivalent symbolic problems. This paper describes a framework to explain these differences developed by analyzing interviews with introductory physics students as they worked on analogous numeric and symbolic problems. It was found that information about the physical situation, as well as the problem solving process are represented in subtly different ways in numeric problems compared to symbolic problems. In almost every respect the inclusion of numbers makes information more transparent throughout the problem solving process. 
Eugene Torigoe
physics.ed-ph