## CHAPTER 3: ADDITION AND SUBTRACTION

**Lesson 1: Solving Problems by Estimating **

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

**Goal**

Estimate sums of 3-digit numbers to solve problems.

**Builds Upon**

Student Book pages 68–69

**Instructions for Use**

**Base Blocks Addition** allows students to solve addition problems by regrouping using base blocks.

To use Base Blocks Addition, scroll down and click on its name. Then click on “Instructions” at the upper right of the new screen and read “Addition exercises” and “Exchanging and grouping pieces”. Click on “Close” at the top when done and then on “Next Problem” at the bottom of the “Solve the problem” column on the right. A new problem will display in the column and also show as base blocks in the 4 place value columns to the left. Add the ones columns by clicking and dragging a rectangle around 10 ones blocks to regroup them as a tens block. Then click and drag this tens block into the tens column. Now add the tens and hundreds columns in the same way as you follow each step in the “Solve the problem” column. You can then click on the up or down “Columns” arrows or on “Next problem” to begin another problem. You can also click on “Create Problem” at top right and then click on and drag blocks into position to make your own problem to solve. Avoid changing the “Dec. Places” and “Base” settings.

**Home Run Derby Math** lets students practice estimating sums and differences.

To use Home Run Derby Math, click on “Play Now” at upper left and then on “Addition” and/or “Subtraction” in the screen that opens. Read the instructions and then click on “Start”. Click on “Play” at the bottom right of the scoreboard that opens and look at the numbers displayed in the “1st” and “2nd” boxes above, and at the “+” or “−“ operation sign on the right. You have 15 seconds to estimate the sum or difference and then click on the “Your answer” box below and type it in. Afterwards, click on “DONE” at bottom right to see the solution. Next, click on “HIT” to see how far your ball went and how close your answer was to the solution. If your answer is not close enough or you fail to answer in time, your at bat will be recorded as a strike. Click on “NEXT AT BAT” at upper right to play another round. The game is over when either you successfully play all 9 innings or record 3 strikes against you. Begin a new game by clicking “Back” and then “Start”.