C. 71.4 days
The half-life of a radioactive sample is the amount of time it takes for half of the sample to decay. Since the sample is 75% decayed after 142.8 days, it means that there is only 25% of the original sample remaining.
Since only 25% of the sample remains after 142.8 days, it must take half of the half-life time for 25% of the sample to decay, which is the definition of the half-life. Therefore, the half-life of the sample is 142.8 days divided by 2, which equals 71.4 days.
What is the half-life of a radioactive sample that is 75% decayed after 142.8 days?
A. 107.1 days
B. 47.6 days
C. 71.4 days
D. 35.7 days
1 answer