# Lesson 10 Add Within 1,000

Let’s find sums within 1,000 and explain our strategies.

## Warm-up Number Talk: Use Sums to Find Sums

Find the value of each expression mentally.

## Activity 1 Card Sort: Three-digit Sums

Sort the cards into 2 groups with your partner.

Make a group of expressions that you agree the value is less challenging to find.

Make another group of expressions that you agree the value is more challenging to find.

Keep any expressions together that you and your partner disagree on.

Choose an expression that you feel is less challenging.

Find the value of the sum. Show your thinking.

Choose an expression that you feel is more challenging.

Find the value of the sum. Show your thinking.

Discuss one card you and your partner disagreed on. If you felt the expression was more challenging, explain why. If you felt the expression was less challenging, explain your method.

## Activity 2 Find the Unknown Value

Oh no! Diego spilled paint on his paper and now he can’t see all the digits in each of his equations.

What three-digit number makes the equation true? Show your thinking.

What three-digit number makes the equation true? Show your thinking.

## Practice Problem

## Problem 1

Find the value of

. Find the missing digit that makes the equation true. Explain how you know.