I think that the answer is C. 10
Wouldn't you do 18.20 divide that by .65 & get 28. So the tool was used for 28 minutes
R=S*0.5^(t/8)
<span>R is the remaining amount </span>
<span>S is the starting amount (500) </span>
<span>0.5^ is for the HALF in half-life </span>
<span>t/8 show that every 8 ts (every 8 hours), it will be halved once </span>
<span>...so plug in 500mg for the general solution... </span>
<span>R=(500)*(0.5)^(t/8) </span>
<span>... plug in 24h to solve for after 24h </span>
<span>R=(500)*(0.5)^(24/8) </span>
<span>R=(500)*(0.5)^(3) </span>
<span>R=(500)*(0.125) </span>
<span>R=(0.0625) </span>
<span>...therefore there with be 0.0625 mg of the dose remaining</span>
