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120 grams of radioactive substance, and now you have 15 grams, how many half lives passed
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37 votes
37 votes
120 grams of radioactive substance, and now you have 15 grams, how many half lives passed

User Chrismit
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1 Answer

14 votes
14 votes

you can use formula:


\tt N_t=((1)/(2)^n)N_o\\\\N_t=final\:mass\\\\N_t=initial\:mass\\\\n=number\:of\:half-life

Input the value:


15=120((1)/(2)^n)\\\\(15)/(120)=(1)/(2)^n\\\\(1)/(8)=(1)/(2)^n\\\\(1)/(2)^3=(1)/(2)^n\Rightarrow \boxed{\bold{n=3\:half-lives}}

User Lgfischer
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