http://www.nipissingu.ca/faculty/danj/educ4274/ASSIGNMENTS/TEACHING%20MATH/S2G2.pdf
http://www.docstoc.com/docs/23899463/Subtraction-With-Regrouping
http://www.scribd.com/doc/60691531/MENINGKATKAN-KEMAHIRAN-MENGUMPUL-SEMULA-DALAM-OPERASI-PENOLAKAN-DENGAN-MENGGUNAKAN-TEKNIK-%E2%80%98CEKAP-PINJAM%E2%80%99
