# Lesson 1 Sums and Differences Within 20

• Let’s find the value of sums and differences mentally.

## Warm-up Number Talk: Subtract Within 20

Find the value of each expression mentally.

## Activity 1 Check Yourself

1. Find the value of each sum mentally.

2. Circle any sum that you did not remember right away.

Write each sum you circled on an index card.

Use the index cards to work on building fluency with these sums.

## Activity 2 Spin and Find the Missing Number

Directions:

• Spin the top spinner to get your total.

• Spin the bottom spinner to get one addend.