Answer:
$54
Step-by-step explanation:
First, we calculate the amount she paid for each pen.
$255/5 = $51
She paid $51 for each pen.
She made a profit of $3 per pen, so she sold each pen for $51 + $3 = $54
Answer: $54
The general way to work this out is to solve the general expression for
the remaining quantity versus half-life, using logarithms. But that's not
necessary with these numbers.
Look at the numbers:
-- 3 mg is 1/4 of 12 mg.
-- 1/4 is the product of (1/2) x (1/2).
-- So the 3 mg is what's left of 12 mg after 2 half-lives.
The 26 minutes must be two half-lives.
-- The half-life of that substance is 26/2 = <em>13 minutes</em>.
Go Maggie !
