A radioactive isotope has a half-life of 120 s. The activity of a sample of this isotope is measured to be A A\,A at a certain time. What was the activity of the sample 240 s earlier?
A4\frac{A}{4}4A
A2\frac{A}{2}2A
2A2A2A
4A4A4A
144 exam-style questions on CIE IGCSE Physics 5.2.4a Half-life. Each one has a worked solution and a mark scheme showing where the marks go.