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Posted by **devin** on Monday, December 5, 2011 at 7:38pm.

- chemistry -
**DrBob222**, Monday, December 5, 2011 at 7:50pm99 what? 99 grams? 99 tons? 99%. I suspect 99%.

Two steps. First determine k.

k = 0.693/t_{1/2}and substitute into the following:

ln(No/N) = kt

I would set No = 100 if that is 99%.

Then N = 1% (if 99% is gone)

k from above

Solve for t in years.

- chemistry -
**devin**, Monday, December 5, 2011 at 8:01pmSorry don't understand it is 99 percent

- chemistry -
**devin**, Monday, December 5, 2011 at 8:09pmLn(100)/1)=(0.693/t^1/2)(t). ??? Don't get it

- chemistry -
**DrBob222**, Monday, December 5, 2011 at 10:58pmThere isn't anything to get. Can you punch the calculator? That's all there is to it. Do it in steps. Don't try to muddle it up by putting all of it together.

ln 100/1 = 4.605

0.693/28.1 = 0.02466 = k

so

ln(100/1) = 0.02466*t

4.605 = 0.02466t

and t = 4.605/0.02466 = ? or about 200 years more or less.

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