so hmmm if we notice, we have 70, 49, 34.3 and so on
so... from 70 to 49, is 21 less
now, what is 21 of 70? well [tex]\bf \begin{array}{ccllll}
amount&\%\\
\textendash\textendash\textendash\textendash\textendash\textendash&\textendash\textendash\textendash\textendash\textendash\textendash\\
70&100\\
21&x
\end{array}\implies \cfrac{70}{21}=\cfrac{100}{x}\implies x=\cfrac{2100}{70}\implies x=30[/tex]
so is 30%, that means 49 is the 70%
ok, now, how much is the 70% of 49? well , simply (70/100)*49, which gives us 34.3
how much is the 70% of 34.3, well 0.7*34.3 or 24.01 and so on
so every day, the wound is shrinking by 30%
thus r=30% or 30/100 which is r = 0.30
[tex]\bf A=P(1-r)^d\qquad
\begin{cases}
d=days\\
A=\textit{current amount}\\
P=\textit{starting value}\\
r=rate\\
----------\\
P=70\\
r=0.30
\end{cases}\implies A=70(1-0.3)^d
\\\\\\
\boxed{A=70(0.7)^d}[/tex]
