# Surf for More Math

## CHAPTER 3: ADDITION AND SUBTRACTION STRATEGIES

**Lesson 9: Estimating Sums and Differences**

Use these interactive activities to encourage students to have fun on the Web while learning about estimating sums and differences. Students can try these activities on their own or in pairs.

**Goal**

Estimate sums and differences using tens.

**Builds Upon**

Student Book pages 76–77

**Instructions for Use**

Estimation Contraption asks students to estimate sums by adding three numbers using each number’s nearest 10. Note that Level 1 is appropriate.

Before the time runs out, estimate the sum using tens. Type your estimate in the box, then click “OK.” When Level 1 is complete, click Estimation Contraption to practise more.

Estimating a Sum allows students to practise estimating sums of 2-digit numbers using tens.

Scroll down the page to the section marked “Practice,” then click “Start.” Read the numbers in the white boxes below, and estimate the sum using tens. Select the sum from the buttons below. Beneath these buttons, a message will appear to tell you if you answered correctly or not. Then read the next problem in the white boxes beneath the “Start” button.