If a drug has a half-life of 2 hours, how many hours are required for the amount to reach 6.25% of the initial dose?

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Multiple Choice

If a drug has a half-life of 2 hours, how many hours are required for the amount to reach 6.25% of the initial dose?

Half-life is the time it takes for the drug amount to drop to half of what’s there. To reach 6.25% of the initial dose, you need four half-lives because (1/2) raised to the 4th power equals 0.0625 (6.25%). With a half-life of 2 hours, four half-lives occupy 8 hours. The remaining amounts after each half-life are: 50% at 2 hours, 25% at 4 hours, 12.5% at 6 hours, and 6.25% at 8 hours.

Half-life is the time it takes for the drug amount to drop to half of what’s there. To reach 6.25% of the initial dose, you need four half-lives because (1/2) raised to the 4th power equals 0.0625 (6.25%). With a half-life of 2 hours, four half-lives occupy 8 hours. The remaining amounts after each half-life are: 50% at 2 hours, 25% at 4 hours, 12.5% at 6 hours, and 6.25% at 8 hours.

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