http://www.speedsums.com

gistfile1.js

function setResult(n){
	var interval = setInterval(
		function(){
			var qe = $('#question');
			var ae = $('#answer');
			var q=qe.text();
			var m = /^(\d+)\s(.)\s(\d+)/.exec(q);
			var v1 = m[1] - 0;
			var op = m[2];
			var v2 = m[3] - 0;
			var a;
			switch(op){
			case 'x':
				a = v1*v2;
				break;
			case '+':
				a = v1+v2;
				break;
			case '-':
				a = v1-v2;
				break;
			case '÷':
				a = v1/v2;
				break;
			}
			ae.val('' + a);
			ae.trigger('keyup');
		},
		30e3/n
	);
	$('#runner').on('runnerFinish', function(){
		clearInterval(interval);
	});
}

setResult(100);