 To Add:
 1st: Represent each addend with tiles.
 2nd: Simplify, if possible, by pairing a positive with a negative to make a zero.
 3rd: What's left is the sum.
ADD.
 Subtraction by "Adding the Opposite"
 1st: Represent the first number, the minuend. Represent the first number.
 2nd: Represent the opposite of the second number.
 3rd: Simplify, if possible, by pairing a positive with a negative to make a zero.
 4th: What's left is the difference.
SUBTRACT.
 Subtraction by "Taking Away"
 1st: Represent the first number, the minuend. Represent the first number.
 2nd: Add enough zeros so the second number may be removed.
 3rd: Remove the second number.
 4th: What's left is the difference.
SUBTRACT.
