A mystery writer who decides the ending of the story then works backward to devise a plot that will lead to the desired conclusion is using a subgoal to solve a problem

TRUE

Explanation:

In psychology, working backwards is used in educational psychology and cognitive science. Working backwards is a problem solving method where an individual already thinks that he has solved the problem and then reverses backwards in his mind to visualize and analyse the solutions for solving the problem.

In the context, the mystery writer ends the story and then works backward to solve the problem and designs a plan and plot to finally arrive to the conclusion of the story.

Hence the answer is TRUE.