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Let's begin with a problem you saw in Session 1, How Long Is a Minute?. You will use the data from this problem to create a stem and leaf plot, a useful device for organizing certain types of data. Note 1
As always, we begin with Step 1 of our four-step problem-solving process:
How good is your sense of time? Without a timing device, how well can you judge the actual length of a minute? Are some people better at judging elapsed time than others?
Twenty-six people tried this activity. At the end of what each person judged to be a minute, the actual time that had elapsed was recorded to the nearest second. The responses (in seconds) were as follows:
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26 Responses to the Question |
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63 |
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67 |
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79 |
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75 |
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57 |
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72 |
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52 |
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89 |
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39 |
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59 |
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55 |
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68 |
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66 |
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86 |
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70 |
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52 |
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60 |
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64 |
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42 |
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54 |
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56 |
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82 |
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57 |
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65 |
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59 |
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33 |
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Note that this is quantitative data, since the responses are numerical values. Time, however, is not obtained by counting as you did when you determined the number of raisins in a box. Time can be measured on a number line, and any point on the line is a possible point in time. The recorded times above were rounded off to the nearest second. But any positive real number is a possible measurement for time. In this way, time is a continuous variable, and data collected on this type of variable are called continuous data. This is in contrast to a discrete numerical variable (like the raisins), which is often obtained by counting and usually assumes only whole numbers as values.
Another example of a continuous variable is height, measured in centimeters. A person's height can be any positive number, even though the data are typically rounded off to the nearest centimeter.
Organizing continuous data, or discrete data with a great deal of variation, often requires that values be grouped.
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