MTH 231

Section 3.2Algorithms for Addition and

Subtraction of Whole Numbers

Overview

• Finally, we spend time on how to add and subtract whole numbers!

• Positional notation, or place value, is the foundation upon which the operations of arithmetic are built.

• The concepts of “carrying” or “borrowing” can be modeled by exchanges.

The Addition Algorithm

• Use mats, strips, and units or base-ten blocks to represent each number.

• Addition, initially, is the process of combining like pieces (mats with mats, strips with strips, units with units).

• Finally, use the facts that 10 units = 1 strip and 10 strips = 1 mat to reduce the number of loose pieces while keeping the same value.

An Example

Another Example

The Subtraction Algorithm

• The “take-away” model of subtraction is utilized.

• Start with the units (the ones place), then work your way to the strips (the tens place), then the mats (the hundreds place).

• If you do not have enough to take away from, exchange with the next object (10 units for 1 strip, 10 strips for 1 mat).

An Example

Another Example