# MathBait™ Multiplication

# Big Numbers

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Transition from 1-digit to 2-digit multiplication with ease! In this activity we explore place value to help students easily transfer their 1-digit multiplication skills, along with the distributive property, to 2-digits!

## Details

Resource Type

Activity

Primary Topic

Multiplication

Unit

3

Activity

18

of

19

So far, we have focused on 1-digit by 1-digit multiplication and multiplication by 10. As we continue in the series, we will soon turn our focus into multi-digit multiplication. This is a great place to see the distributive property in action.

Provide students with a multiplication question such as 5×46. Allow students a moment to consider how they might compute this value. Remind students of the distributive property. Can splitting this up be helpful?

Rewrite the question as 5×(40+6). Ask students how we would utilize the distributive property. Allow them to guide you to 5×40+5×6. Announce we know how to find 5×6, what is it? But how can we find 5×40?

Remind students that 40 is simply saying we have 4 tens. This means 5×40 is asking us how many tens do we have when we skip count by fives, 4 times. Allow students to compute 5×4=20 to conclude the solution is 20 tens. Ask students how we can write the value "20 tens". Help as needed to see that 20 tens is simply placing the 20 in the ten's place. That is 20 tens which equals 200. If students have not yet worked with place value, we recommend waiting to complete this activity and the next until after a unit on place value for the most success.

Avoid encouraging students to "add a zero". This creates a misunderstanding. We are not simply adding a zero, in fact we can't just add values to the end of a number. Instead, we are focusing on placing our value in the ten's place. To do this, we must also place a zero in the one's place as otherwise we wouldn't know if our 20 meant 20 tens or 20 ones.

Now ask students if anyone can think of a different way to approach 4×50. Encourage students to use the distributive property again. Since 50=5×10, this means 4×50=4×5×10 or 20×10. We can count by 20's just like we count by 2's. Have the class count by 20's together: 20, 40, 60, 80, 100, 120, 140, 160, 180, 200. Now we can see that 10 groups of 20 is 200.

Allow students to practice with a partner. Each student will ask their partner a basic fact they have been working on, but with one value changed to tens. For example, rather than asking "what is 3×4?" they might ask what is 3 times 40 or what is 30 times 4. Students can use either "tens" or the distributive property to support them.

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