Aiding a Confused Parent with Arrays

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arrays

Found on Twitter with the caption: “kids can’t learn 6×8= 48 anymore its now 6×8=(5+1)x8 Why the confusing work”

Dear Confused Parent,

The picture you posted comes from a Powerpoint made by EngageNY to help teachers teach Grade 3, Module 3, Lesson 10.  Lesson 10’s objective is to “use the distributive property as a strategy to multiply and divide.”  So the question “How does topic C use the array model to move learning forward?”  is for teachers to consider as they think about the lesson.  The answer EngageNY gives is: “The array model helps students understand division as both a quantity divided into equal groups, as well as an unknown factor problem.”  Which provides important background, but does not directly answer your question.
To get back to the first part of your statement, “kids can’t learn 6×8 = 48 anymore.”  In fact, the Common Core State Standards state that by the end of third grade students should “know from memory all products of two one-digit numbers.”  So they can and should learn 6×8 = 48.  At the same time, they are learning why 6×8 = 48 and how to figure out that 6×8 = 48.
That finally leads us to your question, “Why the confusing work?”  The answer boils down to two main reasons, 1) the distributive property and 2) helping students figure out why 6×8 is 48, based in facts they already know and might be able to do in their head.  The distributive property states that a(b+c) = ab + ac.  The property is important for understanding elementary ideas such as how multiplication and addition are related

5 x 3 = 5(1+1+1) = 5 + 5 + 5

to secondary concepts such as multiplying binomials

(x + 4)(x – 5) = x(x – 5) + 4(x – 5) = x2 – 5x + 4x – 20 = x2 – x – 20.

In the problem you posted, students can break up the array of 48 dots into

(5 + 1)8 = 5 x 8 + 1 x 8 or 6(5 + 3) = 6 x 5 + 6 x 3 to show that they both equal the same number of dots.

This is also a strategy for figuring out 6×8 = 48 if students have forgotten the fact.  They may know 6×5 is 30 and 6×3 is 18 and can add to find 48.  Similarly, they may know 5×8 is 40 and 1×8 is 8 which together make 48 again.  An important part of the Common Core is building fluency through practice and conceptual understanding.  So by the end of third grade they should know

6×8 = 48, but if they don’t we should make sure they have the tools to figure it out.

I hope this makes you feel less confused,

Jim Town – Mathematics Specialist at ACOE Core Learning
Need more Common Core Math help?  Visit our Common Core Math Help page and get your answers today!

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