Competency Based Mathematics for secondary schools is a secondary school Mathematics textbook series which consist of five volumes corresponding to each of the five classes in secondary school. The books are elaborated using the competency-based-approach from a situated perspective (through real life situations). This means that the target is to ensure that the learner possesses the know-how when faced with a daily life challenge or problem.At the end of each module, the learner is expected to have developed competencies which will enable him to use mathematics with confidence to solve some real life problems within a number of domains of life, communicate concisely and unambiguously and develop the power of mathematical reasoning.In book 4, the work begun in the previous levels is revised and developed. Form four being the last but one class before the writing of the GCE, more emphasis is laid towards preparation for the GCE examinations. Throughout the course the learner and the teacher should not take anything for granted even if it appears to resemble what was treated in the previous class. This is because at every level new competencies are introduced and old ones are developed and consolidated in different ways.