Math Strategy: Doubling in Multiplication

Math Strategy: Doubling in Multiplication
Math Strand: Number Sense Multiplication 

Overview:

Students begin to use doubles in the early elementary years when learning addition facts. For example, students are doubling when they compute 3 + 3 = 6, 7 + 7 = 14, and 15 + 15 = 30. Soon they recognize that 3+3=6 is the same as 3 doubled (3 x 2)=6.

A situation where they may repeatedly add could be in a growing pattern.




As students begin to approach more involved math problems, they may accurately use repeated addition but the doubling strategy is more efficient.






Doubling can also occur when students see that a factor in a multiplication sentence can be broke into two equal parts:





The Guide to Effective Instruction in Mathematics Multiplication, Volume 3, page 23, has some information on doubling.

http://eworkshop.on.ca/edu/resources/guides/nsn_vol_3_multiplication.pdf



When students become aware of prime factorization they can use a more advanced form of doubling:



Note: The factors that work most effectively with doubling are 2, 4, 8, 16, 32...

How this supports student learning:

Through doubling, students are beginning to move away from addition and into multiplying. The nature of doubling promotes student thinking about the relationships between numbers.

WHERE TO NEXT?

In the younger years, promote the understanding of doubling when working with addition facts. Use terms like doubles, and two times the amount to connect to multiplication (Proportional Reasoning). Encourage students to use doubling in a ratio table to speed up the process when trying to find a term of a certain value. See if students can determine when doubling will not work in the different doubling situations noted above.


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