Cambridge O Level Additional Mathematics · Syllabus 4037 · Permutations and Combinations
Restricted Selection
What is Restricted Selection?
A selection problem in which the group being chosen must have a stated composition, for example a committee of four containing exactly two students, or a team that must include a particular person. When the objects come from separate groups, the choice within each group is made independently and the separate combination counts are multiplied. When a particular object must be included, it is placed in the group first and the remaining places are filled from the objects that are left; when it must be excluded, it is removed from the pool before counting. Every such problem stays entirely within combinations, since no ordering is involved at any stage.
This definition is part of the Permutations and Combinations chapter in Cambridge O Level Additional Mathematics.