Question

A scientist kept 1,000 grams of a radioactive material in a container. After 66 days, he observed that 125 grams of the radioactive material was left in the container. Based on the observation, which of these is the most likely inference drawn by the scientist?
Select one:
a. About 500 gram of the material decayed in 33 days.
b. About 500 gram of the material decayed in 44 days.
c. About 62.5 gram of the material will be left in the container after 88 days.
d. About 62.5 gram of the material will be left in the container after 110 days.

Answer 1

The sample appears to have gone through 3 half-lives
1st half life: 1000 to 500 g
2nd half life: 500 to 250 g
3rd half life: 250 to 125 g
The duration of a half-life, therefore, can be inferred to be 66 ÷ (3) = 22 days. 

After a 4th half life, there will be 125÷2= 62.5 g. 
At this point, an additional 22 days will have passed, for a total of 88 days.
Answer is C.