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Standard Deviation Formulas

As we know, random variables have few common numerical characteristic – average value, variation and standard deviation. Now we consider standard deviation of the random variable X. 

Sampling (Statistics)

Several boxes of apples are undergoing a quality check. What will be the easiest way to do it? Checking all the apples piece by piece will be time-consuming.

Representing Data

This is the process of selecting samples through different sampling techniques. Then, gather the necessary information. The next step is to organise and present information in a way that can easily analysed and interpreted. 


A histogram is a graph that is made up of vertical lines of equal bases centred at the class midpoints. It is similar to bar charts. However, in bar charts, all bars are the same width in the bar and the height shows the difference.


An average is a value representing a group of data. The common averages are the mean, median and mode.

Cumulative Frequency Graphs

Cumulative frequency is adding up frequencies to provide the running total. It helps us find the median, lower quartile range and upper quartile range in a set of data.


Probability is the likelihood or chance of an event occurring. Probability = the number of ways of achieving success x the total number of possible outcomes.

Cumulative Frequency

This is the running total of the frequencies. On a graph, it can be represented by a cumulative frequency polygon, where straight lines join up the points, or a cumulative frequency curve.