Math Focus 4
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## CHAPTER 3: ADDITION AND SUBTRACTION

### Lesson 2: Estimating Sums

Goal

Estimate sums in different ways.

Instructions for Use

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.”

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.

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.