how to set one field true remaining false at time using boolean

I have 2 models
1. Question
2.Answer
in model mappings like:
class Question
has_many: answers
end
class Answer
belongs_to: answer
end

how to check correct answer in question controller?
EX:
ID 1: QUESTION : 5+5?
ANSWERS: A.5
                  B.8
                  C.9
                  D.10

Question Table:

id   Title

1    5+5?

Answer Table:
+----+--------+------------+-------------+---------------------+---------------------+
|  answer | is_correct | question_id | created_at          | updated_at
+----+--------+------------+-------------+---------------------+---------------------+
       5           0               1
       8           0               1
       9           0               1
       10         1               1

DROPDOWN : D if click D option from dropdown to print correct answer in index.

how will i determine which drop down is selected and how will i get
the value of the drop down that is selected?

In question controller i can handle 2 models Question and Answer
Plese help me!!!

please help me  how to make code in controller !!!! i am new to rails!!!!
Thanks in advance!!!

Last edited by naresh0505 (2013-02-21 00:28:40)