Posted by **Korina** on Saturday, January 29, 2011 at 9:31pm.

If a radioactive isotope has half life of 5 days,how long will it take for its radioactive strength to be a maximum of one thousandth,(1/1000) of its original value?

Can anyone give me a VERY SIMPLE explanation of this please?

Thank you.

- Science -
**drwls**, Saturday, January 29, 2011 at 11:13pm
Solve this equation for the number of days, x:

(0.5)^(x/5) = 1/1000

You can compute x by taking the log of both sides.

x/5 = 9.97

x = 49 days

The words "a maximum of" are not needed in your question. After 49 days, the radioactive strength will be exactly 1/1000 of the original value, except for rounding-off error. You only have one significant figure in the half-life.

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