Lesson 3: Glider Experiment

how they got the number. The teacher may ask questions such as: “how did you get the number? How do you estimate? Why did you choose this number?” Ask them to think about a reasonable procedure in determining the prediction. During the whole class discussion, the teacher may bring this idea to see other students’ opinion on these three strategies.

Table 2.3. Points to discuss

Mode  If there is no same value, what did you do then?

 If there are two values with appeared the same times what did you do?

 The teacher can also relate the mode strategy to the sentences of mode in the first meeting.

Median and Range  What do you think the difference between these two strategies?

 What do you think the strong and weak points of these two strategies?

Mean  How did you find the strategy?

 The teacher emphasizes this strategy for the next meeting.

4. Lesson 3: Glider Experiment (Compensation Strategy on Bar Chart)

students and throw the glider once to show for students how the glider flies. After that, the teacher will show the second throw data as follow:

Table 2.4. The data of throwing the glider

Number of experiments Glider 1

1 110 cm

2 100 cm

In this data, the teacher asks students to find the “typical distance” as the representation of the glider data. The bar chart is used in finding the typical distance (Look the worksheet number 1). The worksheet consists of three questions. The first question is to find the typical distance of the two data above. After that, the data and the typical distance interpret into a bar.

In the second question, the students are given one more addition data, 60 cm. Again, the students are asked to directly interpret the data into the bar and find the typical height. This question emphasizes on the compensation strategy in the bar. The students are expected to realize the strategy to share the amount of value to another value in such a way that the value will result the same. The fourth data, 95 cm, is given as the third question in the worksheet. Interpreting the data into a bar and finding the typical distance from the bar also are the activities in this question. At this time, the students are expected to realize how to find the mean through the compensation strategy in the bar.

Every question is ended with a short discussion on how the students find the typical distance and interpret it into a bar. The discussion stressed at the idea of the average, which add the data and divided them by the

number of data through the compensation strategy on the bar. From the discussion of the first question, the teacher should start to emphasize these points:

a. The strategy between the median and midrange. These two strategies obtain the same answer.

b. The way students draw the bar. How the students put the number on the x-axis and how the length of the bar they drew.

c. The way students draw the typical distance on the bar.

The further discussion also stresses on the points. The formula of mean is introduced implicitly through compensation strategy using the bar chart. Lastly, the students are expected to know how to find the average of the data.

Prediction of students’ responses

Regarding the strategy to get the typical distance, the students may use the median or midrange strategy. The median may take the middle number by dividing the first and the second data. Meanwhile, the midrange uses the maximum and minimum data and divided it by two. These two strategies obtain the same result in the first question, because there are only two data. The strategies do not obtain the same result for the second and the third questions.

In the bar, the students may directly draw the answer without realizing the compensation strategy (figure 2.5.a). They just draw the bar and the typical distance (figure 2.5.b). Similarly, when they ask to explain

their strategy based on the bar (Worksheet 1c, 2b, and 3b), the students may explain based on the median and midrange strategies instead of the compensation strategy.

a

b

Figure 2.5. (a) the bar without compensation strategy;

(b) the bar with compensation strategy

Actions of the teacher

In the typical distance question, particularly for the first question, the students are expected to use the median or midrange strategy. Therefore, when the students use the strategies, the teacher may ask them to present their result during the whole class discussion. It is different with the

second and the third strategies. When they still use the strategies, the teacher encourages the students to realize that the question in the worksheet aims at explaining their strategy based on the bar instead of the data. Since in the whole class discussion for the first question the teacher have already emphasized the compensation strategy, the teacher may post question for students to remember the strategy, “see the first question on how to find the typical distance based on the bar”.

Regarding the interpretation of the bar, the teacher can have a nice drawing of the bar with two colors of markers in the blackboard and starts to ask questions such as: “what do you think we can do to find 105 cm?

What does make the 100 cm bar become 105cm? And what does make 110 cm bar become 105 cm?” The questions support students to realize the compensation strategy which is to give and take some amount of value in such a way that the bar obtains the result values.

Related to the question 1c, 2b, and 3b, the teacher may directly say to the students that the questions need to answer based on the bar instead of the strategy from the data. The teacher may stress from the first question on how to answer such kind of questions.

5. Lesson 4 : Panjat Pinang Context