A radioactive isotope has a half-life of 1,380 years. What proportion of a sample of the isotope would remain after 4,000 years? Give your answer to three decimal places.
A sample of pure cobalt-57 is left in a sealed container for 100 days. At the end of the 100 days, the cobalt is taken out of the container. Its activity is measured and found to be 540 Bq. Cobalt-57 has a half-life of 272 days. What was the activity of the sample at the start of the 100 days? Give your answer to the nearest becquerel.
Carbon-11 has a half-life of 20.3 minutes. The activity of a sample of pure carbon-11 is found to be 7,200 Bq. What will the activity of the sample be 4 hours later? Give your answer to two decimal places.