http://www.kidsmathgamesonline.com/numbers/meanmedianmode.html
http://www.quia.com/rr/51667.html
http://www.superteachertools.com/jeopardy/usergames/Feb201105/game1296561235.php
http://www.bbc.co.uk/bitesize/ks2/maths/data/mode_median_mean_range/play/