Those familiar with introductory algebra will recognize that word problems consist of several conditions that must simultaneously be satisfied. The methods of solving simultaneous equations are then appropriate. Here the common method of elimination by substitution is used. The four simultaneous equations are written. Then the substitutions are done. The process uses mathematics to do mathematics, providing a unified approach to problem solving that spans the curriculum.
The solution starts by responding to what is ASKED FOR: How many does Mary have if she has two more than Tom? One condition.
The starting equation REQUESTS information about the number of apples Tom has. This is stated as 3 times the number Susan has. A second condition.
The resulting equation REQUESTS information about how many apples Susan has. This is stated in the problem as one fourth the number Joe has. A third condition.
Now information is requested about the number of apples Joe has. The problem states that Joe has 4 apples. The fourth condition.
The REQUEST-RESPONSE-RESULT structure is used repeatedly in solving problems.