## Grouped data

To understand a data set with a large number of values, it is helpful both to divide the range of values of the data into intervals, called **class intervals **or classes, and to record the** frequency **of each class interval, the number of data items in each class. The resulting summary of the data is called a grouped frequency table or simply a **frequency table**.

#### Example 3

The marks out of 50 for a mathematics test done by a class of 25 students are:

48 | 43 | 29 | 36 | 37 | 21 | 15 | 24 | 35 | 44 | 37 | 35 | 25 |

29 | 39 | 28 | 25 | 46 | 37 | 24 | 26 | 42 | 45 | 33 | 47 |

Present this information in a frequency table, using groupings of 15–19, 20–24, 25–29 and so on up to 45–49.

#### Solution

Grouping the data produces the following frequency table:

Mark | Tally | Frequency |
---|---|---|

15–19 | 1 | |

20–24 | 3 | |

25–29 | 6 | |

30–34 | 1 | |

35–39 | 7 | |

40–44 | 3 | |

45–49 | 4 |