Step 1
The initial amount of Co-60 = 10.0 g
We need to find the amount of Co-60 left after 1 half-life, 2 and 3 half-lives.
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Step 2
The amount of Co-60 after 1 half-life (n = 1) is:
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Step 3
For 2 half-lives, n = 2 and initial amount = 10.0 mg, the result is: 2.5 mg
For 3 half-lives, n = 3 and initial amount = 10.0 mg, the result is: 1.25 mg
(The same procedure as step 2)
Answer:
How much of a 10.0-mg sample of cobalt-60 is left after one half-life? 5.0 mg
Two half-lives? 2.5 mg
Three half-lives? 1.25 mg