A detector of radioactivity in a laboratory indicates an average background count rate of 12 counts/min12\text{ counts/min}12 counts/min when no radioactive samples are present. A radioactive sample with a half-life of 3.0 hours3.0\text{ hours}3.0 hours is placed near the detector, which then indicates a total count rate of 268 counts/min268\text{ counts/min}268 counts/min.
Calculate the total count rate indicated by the detector 15.0 hours15.0\text{ hours}15.0 hours later.
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.