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Wednesday, September 23, 2015

Math Facts - multiplying by four

This week we reviewed multiplication strategies we learned in 4th grade. Many of us had to "dust off" our multiplication fact knowledge to be successful with multiplying two-digit by two-digit numbers using multiple strategies. 

One of the facts we reviewed was our fours facts. In third grade students learned that if they knew their twos fact (x2 or doubling) they could easily find their fours facts too. 

Let's say I'm trying to solve 4 x 7, but I'm need a strategy to help me solve it, I can use my knowledge of 2 x 7 to help me. I know 2 x 7 = 14 (see below). I've doubled 7 to find my product of 14.


I know can double the product of 2 x 7 to find 4 x 7:

2 x (2 x 7) = 2 x 2 x 7 = 4 x 7
*using the associative property

Fourteen doubled is equal to 28. This is represented in the picture below. 


Why is this important? Fifth graders can apply many of these same strategies to larger numbers. This shows that they can be flexible with their thinking. 


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