Half-life: fraction remaining
A radioactive isotope has a half-life of 8 days. What fraction of a sample remains after 24 days?
Answer D: explanation for every choice
A
This is the fraction after one half-life.
B
This divides by the number of half-lives instead of halving repeatedly.
C
This is the fraction after two half-lives.
D
Correct. 24 days is 3 half-lives, so (½)³ = 1/8 remains.
TakeawayFraction remaining = (½)ⁿ, where n is the number of half-lives.
Equation usedRadioactive decay
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