Topic: Rails custom Form

I am doing an application that loads question database where users answer multiple choice question.
My question model only contains:

      t.integer :user_id
      t.integer :question_no
      t.string :answer
      t.string :score

My question database model contains

      t.integer :question_type
      t.string :topic
      t.integer :difficulty
      t.text :question_text
      t.string :choice1
      t.string :choice2
      t.string :choice3
      t.string :choice4
      t.string :answer

It doesn't make sense to  copy the entire model database to display it when you only need the answer.
However I need to create a form to submit so the user's choice (numerical values delimited by commas) gets saved into question.answer
I also need to replace the show action with the edit action for the form only.
Any ideas how to achieve that?