A radioactive material shows an activity of 4000 Bq at time t=0. After 5 days its activity is found to be 1000 Bq. Ten days after the start, the measured activity is 280 Bq.
(i) Calculate the decay constant of the material.
(ii) Predict the activity that should be present after 10 days based on the first two readings.
(iii) State, with reason, whether the three readings are consistent with the material having a single decay constant.