The half life

The half-life of a radioactive isotope is the time it takes for a quantity of the isotope to be reduced to half its initial mass. Starting with 145 grams of a radioactive isotope, how much will be left after 3 half-lives?

Correct result:

m3 =  18.125 g


m0=145 g q=1/2=12=0.5  m3=m0 q3=145 0.53=1458=1458 g=18.125 g

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