Four days later, Lexi takes 10mg of the same medicine. How much medication, L, is in Lexi’s system on day t?

The new 10 mg dose is taken on day 4, so its decay time on day t is t − 4 days. Using the same half-life model, the amount from this dose is L = 10(1/2)^(t − 4). Choice C has the exponent shifted by 4 days.

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