How to Count Up in Subtraction
When you hear the word "subtraction," you may visualize taking one number, a subtrahend, away from another number. Many students use this method to calculate the difference between two values. Addition requires students to add two numbers. "Counting up," an alternate subtraction method, allows you to use addition to solve subtraction problems. This may seem counter intuitive, but with practice, you can learn to count up and subtract numbers quickly.
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Instructions
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Write down this example subtraction equation:
867 - 254 = X
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Determine the number you must add to the subtrahend, 254, to get it up to the nearest 10. In this instance, you must add 6 to 254. This changes 254 to 260. Draw a circle around 6, the number you added.
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Determine the number you must add to 260 to get it up to the nearest hundred. That number is 40. Circle 40, and add it to 260 to yield 300, the nearest hundred above 260.
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Determine the number you must add to 300 to get it to the largest possible hundred that does not exceed 867. In this example, you must add 500 to 300. The result is 800. Circle 500, the number you added.
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Determine the number you must add to 800 to reach 867. To get from 800 to 867, you must add 67. Circle 67.
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Add the numbers you circled. In this example, those numbers are 6, 40, 500 and 67. The sum of those numbers is 613. The difference between 867 and 254 is 613.
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Tips & Warnings
This example uses 867 as the base number and 254 as the subtrahend. This counting up method works with any two numbers.
References
Resources
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