<SCRIPT>

function testQuestion(question) {
     var answer = eval(question);
     var output = "What is " + question + "?";
     var correct = '<IMG SRC="correct.gif">';

     var response = prompt(output, "0");

     return (response == answer) ? correct : testQuestion(question);
}

</SCRIPT>

<SCRIPT>

var result = testQuestion("10 + 10");

document.write(result);

</SCRIPT>