<style>
#start>div {
display: inline-block;
height: 50px;
width: 150px;
background-color: red;
}
#start>div.active {
background-color: green;
}
</style>
<body>
<div id="start">
<div class="a1">текст 1</div>
<div class="a2">текст 2</div>
<div class="a3">текст 3</div>
</div>
<script src='http://code.jquery.com/jquery-1.9.1.js'></script>
<script>
function next(arr) {
var max = arr.length - 1,
i = -1;
return function () {
i = i < max ? i + 1 : 0;
return arr[i];
};
}
jQuery(function () {
var slider = next($('#start>div'));
var curent;
setInterval(function () {
if (curent) $(curent).removeClass('active');
curent = slider();
$(curent).addClass('active');
}, 1000);
});
</script>
</body>
Пример решения задачи