I understand your desire to help your students become better at solving open response math questions. These problems can be challenging for all students, but especially student good at math. How can that be? These students can have a hard time explaining and writing out steps when the answer just popped in their head.
For those educators for whom this is a new phrase, open response questions in math require students to understand the problem, develop a plan for solving it, solve the problem and check their work, and explain their thinking.
The only way students are going to be good at solving open response math questions, is to do it regularly. Hand them a rubric to help them see when they have successfully solved an open response problem.
Points  Math Open Response Scoring Rubric 

4   Clearly explains thinking by describing steps used to solve the problem, including specific math vocabulary and words from the question
 Shows work which may include computations, diagrams, and/or charts
 Labels parts of the answer
 Computation and answer are correct

3   Clearly explains thinking by describing steps used to solve the problem, including some math vocabulary and words from the question
 Shows some work including computations diagrams, and/or charts
 Labels parts of the answer
 Computations and answer are correct

2   Explanation of thinking is not clear, little writing with no math vocabulary
 Lack of order in computation or does not show work (difficult to follow)
 Answer is not labeled
 Did not answer all parts of the question
 Computations and answer are incorrect

1   No explanation of thinking, no math vocabulary or wrong math vocabulary is used
 Did not follow directions
 Computations and answer is incorrect

0   No explanation of thinking
 Answer is not related to the question
 No work is shown

Revise to fit your needs, but this one way to help your students be independent learners.