Counting on can be used as a strategy to subtract. The video explains how to use a number line to visualize this process. Essentially, instead of counting down, you start at the smaller number (the number being subtracted) and count up to the larger number (the number you're subtracting from). The number of "jumps" or spaces you count represents the difference or answer to the subtraction problem.
Here's a breakdown of how to teach counting on to subtract, based on the information:
Using a Number Line for Counting On
-
Identify the Start and End Points:
- The number being subtracted (the subtrahend) becomes your start point on the number line.
- The number you are subtracting from (the minuend) becomes your end point on the number line.
-
Mark the Points:
- Visually mark both the start and end points on the number line.
-
Count the Jumps:
- Count the number of "jumps" or spaces between the start point and the end point. This is the difference.
Examples
-
Example 1: 11 - 3
- Start point: 3
- End point: 11
- Count the jumps from 3 to 11: 1, 2, 3, 4, 5, 6, 7, 8.
- Therefore, 11 - 3 = 8.
-
Example 2: 14 - 5
- Start point: 5
- End point: 14
- Count the jumps from 5 to 14: 1, 2, 3, 4, 5, 6, 7, 8, 9
- Therefore, 14 - 5 = 9.
Key Considerations
- Visual Aids: Using a number line is crucial, especially when introducing the concept. It provides a visual representation of the counting-on process.
- Start with Smaller Numbers: Begin with smaller numbers to build confidence and understanding before moving to larger numbers.
- Relate to Addition: Emphasize the relationship between subtraction and addition. Counting on is essentially thinking, "What number do I add to the smaller number to get the larger number?"
