Answer:
<h3>After 1st Dose:</h3>As Sophie has just taken the medicine, the quantity of drug present in her body is 500mg
<h3>After 2nd Dose:</h3>
Amount left from 1st dose = 4.5/100 × 500 = 22.5mg
Amount of Drug after 2nd dose = Amount left from 1st dose + 2nd dose taken.
Amount of Drug after 2nd dose = 22.5mg + 500mg
Amount of Drug after 2nd dose = 522.5mg
<h3>After 3rd Dose:</h3>
Amount left from 2nd dose = 4.5/100 × 522.5 = 23.513 mg
Amount of Drug after 3rd dose = Amount left from 2nd dose + 3rd dose taken.
Amount of Drug after 3rd dose = 23.513mg + 500mg
Amount of Drug after 3rd dose = 523.513 mg
<h3>After 4rth Dose:</h3>
Amount left from 3rd dose = 4.5/100 × 523.513 = 23.558mg
Amount of Drug after 4rth dose = Amount left from 3rd dose + 4rth dose taken.
Amount of Drug after 4rth dose = 23.558mg + 500mg
Amount of Drug after 4rth dose = 523.558 mg
<h3>Highest Amount:</h3>
The pattern formed above can be written in the form of sum of finite geometric series:
Sₙ = 500 + 500(0.045) +500(0.045)² + ........................500(0.045)ⁿ
Sₙ = 500(1 + 0.045 + 0.045² ........................0.045ⁿ)
Where
Sₙ = Sum till nth term
a = 500
r = 0.045
As Sophia takes medicines 2 times a day, she takes medicine 20 times in 10 days. So substitute n=20 in the formula for the sum of finite geometric series
Greatest amount of antibiotic present = 523.5602 mg
This amount is almost constant after 3rd dose, so it will occur after every dose after 3rd dose
<h3>Drug present in body at different points:</h3>
After 1st dose = 500mg
After 2nd dose = 522,5mg
After 3rd dose = 523.513 mg
After the the amount left in the body almost remains constant.
Which means that after each dose, the amount in body is maximum, at the end of the 12 hours, the amount reduces to 4.5%, which reaches almost the same maximum after taking another dose.