Repeated random number questions

I have the following class which needs to display random questions to the user.

However my issue is that the class displays only one question rather than asking questions continuously . How can I repeat user questions in order to keep their! score? See image below -

public class Chooser extends ActionBarActivity implements View.OnClickListener {

    int randomOne = 0;
    int randomTwo = 0;
    int problems = 0;
    int sum = 0;
    int userAnswer = 0;
    int correct = 0;
    int inCorrect = 0;
    int userInput, result;

    TextView question, response, answer, report;
    EditText userNumber;
    Button ans;
    private Random add;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chooser);

        question = (TextView) findViewById(R.id.question);
        response = (TextView) findViewById(R.id.response);
        answer = (TextView) findViewById(R.id.answers);
        report = (TextView) findViewById(R.id.report);
        userNumber = (EditText) findViewById(R.id.answer);
        ans = (Button) findViewById(R.id.button);
        ans.setOnClickListener(this);
        add = new Random();
        randomOne = add.nextInt(20);
        randomTwo = add.nextInt(10);
        Display();

    }

    public void Display() {
        sum = randomOne + randomTwo;
        question.setText(randomOne + " +  " + randomTwo);
    }

    @Override
    public void onClick(View v) {
        userInput = Integer.parseInt(userNumber.getText().toString());
        Log.e("getting user input", "" + userInput);

        if (userInput == sum) {

            response.append(" CORRECT! , You are the best \n");

            correct++;
        } else {

            response.append("INCORRECT, The correct answer was  :" + sum + "\n");

            inCorrect++;
        }

        problems++;


    }


}