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OpenStudy (anonymous):
the half life of a certain substance is 25 years. How long will it take for a sample of this substance to decay to 90% of its original amount
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OpenStudy (anonymous):
10% = 1/2^n where n is number of half lives to reach 10% --> n = ln10/ln2 and multiply by 25 gives 83.05 years to 2dp
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