A Level Computer Science OCR Practice Exam

How can the AND's and OR's be manipulated in boolean expressions?

1. They cannot be switched

2. They can be arbitrarily switched without changing results

3. They can be switched only in certain conditions

4. They can only be switched when negated

The correct answer is: They can be switched only in certain conditions

The correct understanding of how AND and OR can be manipulated in boolean expressions is that they can indeed be switched, but only under certain conditions, which is why the chosen answer is accurate. In boolean algebra, the manipulation of ANDs and ORs follows specific rules, such as the commutative and associative laws. For example, in expressions like A AND B is equivalent to B AND A and A OR B is equivalent to B OR A, allowing for switching without changing the result. However, in complex expressions, particularly when negations (NOT operations) are involved, switching AND and OR may not yield the same result. This is due to laws like De Morgan's which apply to combinations of terms. When negations are introduced, the way terms are grouped and operated on becomes essential to ensure the outcome remains consistent. Thus, the claim that they can be switched only under certain conditions aligns perfectly with the principles of boolean algebra, which acknowledges the role of terms within expressions influenced by negation and logical grouping.