A Geiger-Müller (GM) tube is used to monitor the activity of a radioactive isotope in a laboratory. The average background count-rate in the room is measured to be 24 counts s−124\text{ counts s}^{-1}24 counts s−1. With the source in place, the initial measured count-rate is 280 counts s−1280\text{ counts s}^{-1}280 counts s−1. The radioactive isotope has a half-life of 8.0 hours8.0\text{ hours}8.0 hours.
What is the expected total count-rate registered by the GM tube after 32.0 hours32.0\text{ hours}32.0 hours?
16 counts s−116\text{ counts s}^{-1}16 counts s−1
17.5 counts s−117.5\text{ counts s}^{-1}17.5 counts s−1
40 counts s−140\text{ counts s}^{-1}40 counts s−1
88 counts s−188\text{ counts s}^{-1}88 counts s−1