(a) Explain what is meant by the critical region of a statistical test.
Under a hypothesis \(\mathrm { H } _ { 0 }\), an event \(A\) can happen with probability \(4 \cdot 2 \%\). The event \(A\) does then happen. State, with justification, whether \(\mathrm { H } _ { 0 }\) should be accepted or rejected at the \(5 \%\) significance level.