Lets do the working for the amount of medication remaining in Noelle's body.
Day 1:
600 × 0.6 = 360
Day 3:
360 × 0.6 = 216
Day 4:
216 × 0.6 = 129.6
Day 5:
129.6 × 0.6 = 77.76
By the time Karey is taking the medication, Noelle only has 77.76 in her body.
This expressed as a percentage in relation to Karey's amount is :
77.76/600 × 100 = 12.96%
= 12.9%
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