- Before collection of data, we need to identify what we would use it for.
- The data that is collected needs to be organized in a proper table, so that it becomes easy to understand and interpret.
**Average**is a number that represents or shows the central tendency of a group of observations or data.**Arithmetic mean**is one of the representative values of data.- Mean = (sum of all observatory) / (Number of observatory)
- Mean of data may or may not be from given data.

**Mode**is another form of central tendency or representative value.- The mode of a set of observations is the observation that occurs most often.
- If each of the value in a data is occurring one time, then all are mode.
- Sometimes we also say that this data has no mode since none of them is occurring frequently.

**Median**is also a form of representative value.- It refers to the value which lies in the middle of the data with half of the observations above it and the other half below it.
- Median = ½ [ n/2 th observation + (n/2 + 1)th observation ]

- A bar graph is a representation of numbers using bars of uniform widths. Double bar graphs help to compare two collections of data at a glance.
- Double bar graphs help to compare two collections of data at a glance.
- There are situations in our life, that are certain to happen, some that are impossible and some that may or may not happen. The situation that may or may not happen has a chance of happening.
**Probability**is the branch of mathematics that is used for calculating the likelihood of an event taking place.- If you have 10 likelihoods and you want to calculate the probability of 1 event taking place, it is said that its probability is 1/10 or event has a 10% probability of taking place.
- Events that have many possibilities can have probability between 0 and 1
- Total probability of occurrence of any universal event is sum of its all the sub events and is equal to 1.