

 A radioactive substance has a halflife of 30 minutes.
What fraction of the atoms will not have decayed after
1 hour?
click
for answer
 Another substance has a halflife of 3 hours.
What fraction of the atoms will have decayed after 6 hours?
click
for answer
 A researcher measures 200 counts per minute coming from a radioactive
source at midday.
At 3 o'clock, she finds that this has dropped to 25 counts per
minute.
What is the halflife of the radioactive source?
click
for answer


