The following video clearly describes how to find the mean and the standard deviation of a set of data. You may watch more than once to get a clear idea of the use, after which it will become quite natural to you.

Mean, μ = Σx/n where n is the number of data; Standard Deviation, σ = Σ(x-μ)^{2}/n

The following video clearly describes how to find the mean and the standard deviation of a set of data in a table. You may watch more than once to be familiar with entering data in a table.

Mean, μ = Σfx/Σf where f is the number of data of each class; Standard Deviation, σ = Σf(x-μ)^{2}/Σf

This is a vast collection of tutorials, covering the syllabuses of GCSE, iGCSE, A-level and even at undergraduate level.
They are organized according to these specific levels.

The major categories are for core mathematics, statistics, mechanics and trigonometry. Under each category, the tutorials are grouped according to the academic level.

This is also an opportunity to pay tribute to the intellectual giants like Newton, Pythagoras and Leibniz, who came up with lots of concepts in maths that we take for granted today - by using them to serve mankind.

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Vivax Solutions, while mimicking nature, offers a huge set of tutorials along with interactive tools for free.

Please use them and excel in the sphere of science education.

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Maths is challenging; so is finding the right book. K A Stroud, in this book, cleverly managed to make all the major topics crystal clear with plenty of examples; popularity of the book speak for itself - 7^{th} edition in print.