# Section A: Practice Problems Add and Subtract

## Section Summary

Details

In this section, we used addition and subtraction to compare and to find unknown values. We used different tools to show how to add and subtract two-digit numbers.

We learned that when you subtract 2 two-digit numbers you can think about subtracting tens from tens and ones from ones.

## Problem 1 (Pre-Unit)

There are 17 squirrels in a pine tree. There are 12 squirrels in an oak tree.

1. How many fewer squirrels are in the oak tree than in the pine tree? Show your thinking.

2. Write an equation for this situation.

## Problem 2 (Pre-Unit)

Fill in the blank to make each equation true.

## Problem 3 (Pre-Unit)

There are some frogs in the pond. Then 5 more frogs jump into the pond. Now there are 11 frogs in the pond. How many frogs were in the pond? Show your thinking.

## Problem 4 (Lesson 1)

Here are some connecting cubes.

1. How many connecting cubes are there altogether? Show your thinking.

2. How many more cubes are there in train 1 than in train 2? Show your thinking.

## Problem 5 (Lesson 2)

Find the number that makes each equation true in a way that makes sense to you. Show your thinking.

## Problem 6 (Lesson 3)

There are 34 children in Mai’s classroom. There are 21 children in Noah’s classroom. How many more children are in Mai’s classroom than in Noah’s classroom? Show your thinking using drawings, numbers, or words and write an equation.

## Problem 7 (Exploration)

Jada added 3 different numbers between 1 and 9 and got 20.

1. What could Jada’s numbers be? Give three different examples.

2. If Jada used 6, what are the other two numbers? Explain your reasoning.

## Problem 8 (Exploration)

1. Make a list of 10 pairs of numbers that add together to make 100.

2. What patterns do you notice in your pairs of numbers?

## Problem 9 (Exploration)

Tyler likes representing addition using base-ten blocks. Here is how Tyler represented a sum.

1. How can Tyler’s base-ten blocks help to find the solution to the equation ?

2. What other addition equations could Tyler’s cubes show?

3. What could he do to make his meaning clearer?