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4-7, 13+

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## Addition of Decimal Numbers and a Common Error

Students practice carefully lining up decimal places while calculating sums of decimals that total more than one.

### Overview

Students are asked to calculate sums of decimals that total more than one, carefully lining up decimal places. This CYBERCHASE activity is motivated by two video clips in which the characters calculate sums involving decimals, but in each case there is an error in the decimal point placement, once by right-justifying a whole number, and the second by ignoring the decimal place.

4-7

### Suggested Time

60 minutes

### Media Resources

How Many Rails for the Detour? QuickTime Video
How Far to Wells Road? QuickTime Video

### Part I: Learning Activity

1. Have the students work in pairs for this activity.

2. Tell students that they will watch a video clip in which the CyberSquad solve a problem by building a detour around an obstacle.

3. Show students the first part of the How Many Rails for the Detour? QuickTime Video and pause it after Jackie makes her first calculation.

4. Distribute Handout 1: "How Many Rails for the Detour?"   and ask the students to work the problem (the same problem that Jackie works in the video clip).

5. Ask the students whether they agree with Jackie's calculation, and why or why not. Tell them that they will now watch the rest of the video, to see how Digit does the calculation.

6. Show students the rest of the How Many Rails for the Detour? QuickTime Video .

7. Discuss the importance of keeping the decimal places lined up when adding or subtracting decimals.

8. Distribute Handout 2: "How Far to Wells Road?"  and ask them to work the problem.

9. Tell the students that they will now watch a video from "Cyberchase For Real" in which Bianca drives to a friend's house.

10. Show students the How Far to Wells Road? QuickTime Video .

11. Ask the students to compare their results with Bianca's, and to discuss why Bianca's answer was incorrect.

12. Distribute Handout 3: "Errands" . The handout shows a map of a set of places Marty goes to do his errands. The students are asked to find the total distance traveled and to compare it to an alternative route home.

### Part II: Assessment

Assessment: Level A (proficiency): Students are asked to add several whole numbers, and then to add several decimals. They are asked to compare their strategies.

Assessment: Level B (above proficiency): Students are asked to find the totals of the three highest long jumps for each of 3 athletes, and then rank the 3 athletes' total scores as first, second, and third place.

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