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In this lesson, we will learn how to apply the associative property of addition of three numbers whose sum is, at most, 20.

Q1:

Rania has 20 counters.

Use the counters to find the missing number.

Q2:

Find the missing number in 1 6 + 3 + 1 = + 1 .

Using that 1 6 + 3 + 1 = 1 9 + 1 , what is 1 6 + 3 + 1 ?

Q3:

Maged had 5 chocolate bars, 4 lollipops, and 3 gummy bears.

In total, he had candies.

Find another way to write the total number of candies.

Q4:

Find the missing number in 1 3 + 4 + 7 = + 7 .

Q5:

We will see how we can write 4 + 6 + 3 in different ways.

Find the missing number.

Complete the missing sum.

All of these sums are equal. What are they equal to?

Q6:

When we add three numbers, we can first add any two of them.

For example, to find 8 + 6 + 7 , we could first add 8 and 6 to get 14 as the picture shows.

Now, can you find the missing number?

Q7:

Q8:

Am I using the equal sign correctly? Check if the two sums are equal.

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