The collection, recording and presentation of data help us organise our experiences and draw inferences from them. In chapter 3 Data handling, you will learn about different kind of graphs and data. Now let us discuss the methodical procedure to follow before documenting data and extracting information from them.

- We should know what we would use the data for before collecting them.
- The collected data needs to be organised in a proper table so that it becomes easier to interpret and understand the data.

## Representative Values

Let us consider that you want to know the weather in Delhi. On the internet, you would find the temperatures in Delhi for a lot of days like the data of the temperature in the past and the data of the temperature in the present and also the predictions of the temperature in the future. This would lead to a lot of confusion, right? Instead of this long list of data, mathematicians decided to use representative values which could take into consideration a wide range of data. The various types of representative value used by mathematicians in Data Handling are:

- Arithmetic Mean
- Mode
- Median

**Arithmetic Mean**– A number that is obtained by dividing the sum of the elements of a set by the number of values in the set is known as the arithmetic mean. To better understand, let us look at the below example. It measures the central tendency of a set of data. A**range**is a difference between the highest and the lowest observation that gives us an idea of the spread of the observations.**Mode**– It shows the central tendency of a group of observations or data. The mode of a set of observations is the observation that occurs most often. Let us look at the below example to better understand mode.**Median**– A representative value that refers to the value that lies in the middle of the data with half of the observations above it and the other half below it.

## Use of Bar Graph

The representation of numbers using bars of uniform widths is known as bar graphs. Let us look at an example of bar graph given below,

A double bar graph is used to compare two collections of data at a glance. Let us look at the below example, to better understand.

## Class 7 Maths Lines And Angles Important Questions

- Organise the following marks in a class assessment, in a tabular form.

4, 6, 7, 5, 3, 5, 4, 5, 2, 6, 2, 5, 1, 9, 6, 5, 8, 4, 6, 7

- The rainfall (in mm) in a city on 7 days of a certain week was recorded as follows:

Day |
Mon |
Tue |
Wed |
Thu |
Fri |
Sat |
Sun |

Rainfall (in mm) |
12.2 | 0.0 | 20.5 | 5.5 | 1.0 | 2.1 | 5.5 |

Find the range and mean rainfall for the week.

- The weights (in kg.) of 15 students of a class are:
**38, 42, 35, 37, 45, 50, 32, 43, 43, 40, 36, 38, 43, 38, 47**

**(i)** Find the mode and median of this data.

**(ii)** Is there more than one mode?

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