Here some recommended exercises to work:
http://ww2.college-em.qc.ca/prof/epritchard/countnc.htm
http://www.eflnet.com/grammar/muchmany1.php
http://www.english-4u.de/how_much_many_ex1.htm
http://www.englishexercises.org/makeagame/viewgame.asp?id=2134