Maybe one to one is better. each question is mapped in the other table to one row with all the answers:
class Questions
{
/**
* @ORM\OneToOne(targetEntity="Answers", mappedBy="questions")
*/
private $answers;
class Answers
{
/**
* @ORM\OneToOne(targetEntity="Questions", inversedBy="answers")
* @ORM\JoinColumn(name="question_id", referencedColumnName="id")
*/
private $questions;