# Lesson 12 Equations with Unknowns

Let’s represent equations with a ? for the unknown.

## Warm-up True or False: Making Tens

Decide if each statement is true or false. Be prepared to explain your reasoning.

## Activity 1 Number Line Riddles

Solve riddles to find the mystery number.

For each riddle:

Write an equation that represents the riddle and write a ? for the unknown.

Write the mystery number. Represent the equation on the number line.

I started at 15 and jumped 17 to the right. Where did I end?

Equation:

Mystery number:

I started at a number and jumped 20 to the left. I ended at 33. Where did I start?

Equation:

Mystery number:

I started on 42 and ended at 80. How far did I jump?

Equation:

Mystery number:

I started at 76 and jumped 27 to the left. Where did I end?

Equation:

Mystery number:

I started at a number and jumped 19 to the right. I ended at 67. Where did I start?

Equation:

Mystery number:

I started at 92 and ended at 33. How far did I jump?

Equation:

Mystery number:

## Activity 2 Make the Equations True

Find the number that makes each equation true.

Show your thinking on the number line.

## Practice Problem

## Problem 1

I started at a number on the number line and jumped back 37. I landed at 26. Where did I start?

Write an equation with a ? for the unknown.

Find the number that makes the equation true.

Represent your thinking on the number line.