## CHAPTER 3: ADDITION AND SUBTRACTION

**Lesson 2: Estimating Sums **

**Goal**

Estimate sums in different ways.

**Instructions for Use**

**The Addition Machine**

To use The Addition Machine, scroll down the central list and click on its name under “*Skills practice programs, games, and puzzles*”. On the new screen that displays, read the instructions and choose Level 3. Estimate first, then solve the problem that appears by adding from left to right, clicking on the empty box right of the equals sign, and typing your answer. Then click on “Check my answer”. If it is right, “Well done!” will display to its right and the score below will show the number value of the answer and “1” under “Correct”. If not, “Try again” will display and the score will be less the number value of the answer and show “1” under “Incorrect”. Correct the answer and click on “Check my answer” again to get back your lost number value. Then begin a new round by clicking on Level 3 again. Your score will go up with every correct answer and down with every incorrect answer that you do not correct before starting another round.

**Addition of Three-Digit Numbers**

To use Addition of Three-Digit Numbers, read the directions at top and click on “New Problem” at lower right to begin. Type any number between 1 and 999 in the empty box on the left of the “+” sign above and hit “Enter” on your keyboard. The number will appear as base blocks to the left and in place value columns below. Do likewise for the empty box to the right of the “+” sign and watch as your second number appears below the first. If any column has more than 9, click on “Regroup” and watch as the numbers and blocks regroup. Continue regrouping until the column totals are all 9 or less, and then click on “Check”. If you have regrouped all the columns you will see “Great job! Click on New Problem to start over.” If not you will see “Keep going. More regrouping is needed.”

**Addition to 1000 (2 min)**, **Addition to 1000 (1 min) **, and **Addition to 1000 (30 s)**

To use any site, read its instructions. Make sure that the “Num Lock” key on your keyboard is on and then double click in the coloured problem area to start the timer. Add the numbers mentally from right to left and type in your answer, starting with the hundreds digit first, by using the number keys at the right of your keyboard. Backspace over any mistyped numbers and correct them, and then press “Enter” on your keyboard. A score sheet at the lower left of the problem area shows your time remaining in seconds and the number of problems you have answered correctly and incorrectly. See how many problems you can get correct in the time available, and then click on the yellow bar below to start a new round.

**Base Blocks Addition**

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**

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”.