[1]
Croft, T. and Davison, R. 2010. Foundation maths. Prentice Hall.
[2]
Croft, T. and Davison, R. 2010. Foundation maths. Pearson/Prentice Hall.
[3]
Rosen, K.H. and Krithivasan, K. 2013. Discrete mathematics and its applications. McGraw-Hill.
[4]
TheMathPage Skill in Algebra: http://www.themathpage.com/alg/algebra.htm.