 Math Focus 3  Student Centre • Surf for More Math • Try It Out • Web Quests  Teacher Centre  Parent Centre     ## CHAPTER 3: ADDITION AND SUBTRACTION STRATEGIES

### Lesson 9: Estimating Sums and Differences

Goal

Estimate sums and differences using tens.

Instructions for Use

Estimation Contraption asks you 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 you 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.   