The hints for this self review exercise for negative numbers is based upon the concept of zero pairs.
Note on conceptual representation of numbers using discs based on zero pairs:
Blue represent positve numbers : 6 - 3 (6 blue discs minus 3 blue discs)
Red represent negative numbers : minus 3 blue discs is converted to 3 red discs
ie - 3 = (-3)
So 6 - 3 = 6 + (-3)
= 3 + 3 + (-3)
= 3 + (3 - (-3)) zero pairs in brackets
= 3
Version 2 omits addition and subtraction of positive only numbers with positive results.
