Math strand - Number Sense
Overview:
Repeated subtraction is the process of subtracting the same number from another number two or more times until 0 is reached. This strategy specifically supports division. To use this strategy, you take the dividend and repeatedly take the divisor away from it.
On the Lawson continuum, it is located in the Working With Numbers section.
Students may begin using repeated subtraction with manipulatives and then transfer this strategy to working with numbers. See video below:
With smaller numbers, this strategy is fairly efficient and effective. However, as students progress to larger numbers this can become challenging and inefficient.
How this supports student learning:
Repeated subtraction helps prepare students for the strategy partial quotients where they are taking off chunks of the dividend. When students are comfortable subtracting from larger numbers down to 0 with a constant amount, they will better understand how to subtract from larger numbers in different sized chunks. Below is an example of partial quotients to help you better understand.
Where to next?
Once students are comfortable with the repeated subtraction strategy, they should move towards practising partial quotients, which involves students solving a division problem by subtracting multiples until they get down to 0, or as close to 0 as possible. The subtraction of friendly multiples is key, such as using 5, 10, 25, 100 etc. Students will then add the multiples up to find the answer.
An activity that might help to support repeated subtraction would be simple subtraction activities from the Guides to Effective Instruction, such as any of the Learning Connections from the Counting unit, starting on page 143.
http://oame.on.ca/eduproject/ontariomathedresources/files/Number%20Sense%20and%20Numeration%201-3%20Revised.pdf
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