Addition and Subtraction Strategies

The first part of our mathematics journey this year has been to deepen our understanding of place value and number sense through exploring addition and subtraction. We have built upon many mathematical ideas learned in 3rd grade in order to find more efficient ways to solve problems involving larger numbers as 4th graders.

Decomposing

This helpful strategy helps us "see" the value of each digit so that we can make sense of combining and separating numbers because each part of the problem is broken down into its place value "parts". An addition (combining) example is shown below.

Compensation

This awesome strategy is useful when one of the numbers we are computing with is near a landmark number.
When adding, we might take one from the second addend and combine it with the first addend to make an "easier" problem.

When subtracting, we might adjust both the subtrahend and minuend by the same amount (keeping their distance/difference the same) so that we can subtract easily (without regrouping).

There are also other ways to compensate when adding and subtracting- these are just two examples.

Straight Subtraction

This strategy reminds us that we can NOT just switch digits around among our minuend (whole) and subtrahend (part) when subtracting (even though we might want to in order to make subtraction easier). We CAN subtract larger numbers from smaller numbers...we just end up with negative numbers that need to be dealt with.

 

Traditional Algorithm & the Expanded Algorithm

Decomposing each number to be computed into its place value parts helps to show HOW the traditional algorithm works. This works well with both addition and subtraction. A subtraction example is shown below.

We will continue to explore a variety of strategies when adding and subtracting numbers to the millions throughout the course of the school year.

 

Students, what is your favorite strategy?
Leave a comment and let us know.