There are too many softwares which are useful for numerical calculation but most of them are not free. They have high price and most of the student from developing country can not afford them. But don't worry. There are some useful tools which will provide you a better platform to learn numerical computing. Here I'm talking about a Scilab. Scilab is open source software so you can use it freely. 
There is an article about Scilab in Wikipedia.  In this article Scilab is introduced as 
Scilab is an open source, cross-platform numerical computational package and a high-level, numerically oriented programming language. It can be used for signal processing, statistical analysis, image enhancement, fluid dynamics simulations, numerical optimization, and modeling and simulation of explicit and implicit dynamical systems. MATLAB code, which is similar in syntax, can be converted to Scilab. Scilab is one of several open source alternatives to MATLAB.
I have tried Scilab. It is different from Matlab which is another software for scientific computing. Main benefit of 
Scilab is it is free software.Once you learn Scilab there will be not difficult to learn Matlab because both are numerically oriented programming language. There are some basic difference between Matlab and Scilab. You can read here about the differience.
You must be interested about using Scilab right now. You can download it freely from here.
In beginning there will be difficult to use Scilab. You may need help about it.
You can search  for manual and tutorial. Scilab itself provide a manual. You can download it from here. 
I hope this article will help you to understand about Scilab and you will enjoy numerical computing software.