Lesson 9 Add Three-digit Numbers

- Let’s practice adding within 1,000.

Warm-up Number Talk: Ten and Some More

Find the value of each expression mentally.

$528 + 2$
$528 + 7$
$487 + 3$
$487 + 8$

Activity 1 How Did You Add Three-digit Numbers?

Find the value of each expression. Show your thinking.

$384 + 409$
$757 + 152$
$262 + 438$
$575 + 166$

Activity 2 Analyze and Add

Two students talking.

Noah and Kiran showed how they found the value of $267 + 338$ .

Noah’s work

Base ten diagram. 5 hundreds labeled 500. 9 tens labeled 90. 15 ones, 10 circled, labeled 10, 5 labeled 5.

Kiran’s work

How is Noah and Kiran’s work the same? How is it different?
Which student found the correct value? Explain or show your thinking.

Practice Problem

Problem 1

Here is how Jada found the value of $741 + 179$ .

$741 + 9 = 750$

$750 + 100 = 850$

Explain Jada’s error.
Correct Jada’s work and find the value of $741 + 179$ .