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The half-life of a radioactive isotope is 20 minutes. What is the total amount of 1.00 g of sample of this isotope remaining after 1 hour?

User Matewka
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So since every 20 mins the mass will be cut in half (and that happens 3 times), you have just got to divide 1g by 2, 3 times.

after 20 mins the mass will be .5

after 40 mins the mass will be .25

Answer: After 1 hour the mass will be .125g
User MIH
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