@book{1920,
	author = {Haylock, Derek. and Thangata, Fiona. and ebrary, Inc.},
	title = {Key concepts in teaching primary mathematics},
	publisher = {SAGE,},
	year = {2007.},
	series = {SAGE key concepts},
	address = {Los Angeles ;},
	url = {http://site.ebrary.com/lib/rucke/Doc?id=10285279}
}