From a list to classes
Show on a big screenTwenty readings are too many to read one by one. To tally is to count with one mark per reading.
- Twenty readings, scattered on the minutes line.
- Four equal classes, width 10, drawn over them.
- Tally each reading. Bars rise to 8, 5, 4, 3.
Classes
Here are 20 made-up readings. Each one is minutes played outside.
| Reading |
|---|
| 7, 12, 3, 0, 25, 18, 9, 31, 14, 6, 22, 27, 5, 11, 38, 16, 2, 20, 33, 8 |
No reading repeats, so one row per value gives twenty rows. Group them into spans instead. Each span is a class. In the class 10-20, the lower bound is 10. The upper bound is 20. Books also say lower limit and upper limit. The jump between lower bounds is the class width. Here it is 10. Your book also calls it the class size.
A boundary is a number where two classes meet. A reading on a boundary goes in the class above. So 10 is in 10-20, not in 0-10.
| Minutes played | Frequency |
|---|---|
| 0-10 | 8 |
| 10-20 | 5 |
| 20-30 | 4 |
| 30-40 | 3 |
The number of readings in a class is its frequency. The frequencies add up to 20.
Pick a class width. Write classes with no gaps. Count each reading into one class. A reading on a boundary goes in the class above. The frequencies add up to the number of readings.
In this lesson every class has the same width, 10.
Example: 38 is at least 30 and less than 40. So it goes in 30-40.
Now tally eight readings yourself.
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Try the lab to finish this lesson.