Radioactive nitrogen-13 has a half-life of 10 minutes. After 40 minutes, how much of this isotope would remain in a sample that originally contained 96 mg

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After 40 minutes, which is 4 half-lives of nitrogen-13 (10 minutes per half-life), the amount of the isotope would have halved 4 times. Starting with 96 mg, after one half-life (10 minutes), it would be 48 mg; after two half-lives (20 minutes), it would be 24 mg; after three half-lives (30 minutes), it would be 12 mg; and after four half-lives (40 minutes), it would be 6 mg.

Radioactive Nitrogen-13 Has a Half-Life of 10 Minutes