To achieve 100% statement coverage and 100% decision coverage for the provided pseudo code, at least two test cases are required. The first test case should cover the scenario where X > Y, which will execute the statements in the "if" branch. The second test case should cover the scenario where X Y, which will execute the statements in the "else" branch. This ensures that both the true and false branches of the decision are tested, and all statements in the code are executed at least once.
Reference: The ISTQB CTFL Syllabus, version 4.0, discusses the need for different test cases to ensure statement and decision coverage.