SOLUTION: The half-life of a radioactive element is 5 days. How long will it a 1000 g sample to decay to 62.5 g? 15 days 20 days 2.5 days 5 days 10 days

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Question 1162733: The half-life of a radioactive element is 5 days. How long will it a 1000 g sample to decay to 62.5 g?

15 days

20 days

2.5 days

5 days

10 days

Found 2 solutions by ikleyn, greenestamps:
Answer by ikleyn(52832)   (Show Source): You can put this solution on YOUR website!
.

     = 500 g  after 5 days  (one half-life period);


     = 250 g  after 10 days  (two half-life periods);


     = 125 g after 15 days    (three half-life periods);


     = 62.5 g after 20 days   (four half-life periods).


ANSWER.  20 days, or 4 (four) half-life periods.

From my post,  you see that the answer can be obtained  MENTALLY.

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See the lesson
    - Radioactive decay problems
in this site.



Answer by greenestamps(13203)   (Show Source): You can put this solution on YOUR website!




So 4 half lives = 4*5 days = 20 days


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