The correct answer is c) 45 hours.
In the first half-life, half of the sodium-24 decays, so only 1/2 remains.
In the second half-life, half of the remaining sodium-24 decays, so 1/2 * 1/2 = 1/4 remains.
In the third half-life, half of the remaining sodium-24 decays, so 1/2 * 1/4 = 1/8 remains.
Since the half-life of sodium-24 is 15 hours, after 3 half-lives (3 * 15 = 45 hours), only one-eighth of the sodium-24 remains.
Sodium-24 has a half-life of approximately 15 hours. If only one-eighth of the sodium-24 remains, about how much time has passed?
a
15 hours
b
60 hours
c
45 hours
d
30 hours
1 answer