$('button').on('click', function() {
var id = $(this).attr('id');
$('select').val(id);
});
<select>
<option value="a">a</option>
<option value="b">b</option>
<option value="c">c</option>
</select>
<button id="a">a</button>
<button id="b">b</button>
<button id="c">c</button>