From \emph{Swan Boats at Four}, a novel by George V. Higgins.

\begin{quotation}
Rutledge said ``In other words, if we'd painted over that damned
picture in the summer of nineteen seventy-eight, we would've made the
club, and ourselves individually, liable for a hundred thousand bucks,
plus interest at, say, an average of seven percent per annum,
compounded for thirty-four years. \ldots''

``Offhand,'' [David] said, ``I can't even imagine how much that
would've been.'' 

``At the time, I couldn't either,'' Rutledge said, `` \ldots so we
looked it up --- I don't mean we figured it out. \ldots I don't
recall the exact figure, but it came out to around a million and a
half dollars.''%
\begin{csmr}
George V. Higgins, 
\emph{Swan Boats at Four},
Henry Holt and Company, 1995,
pp. 198-199.
\end{csmr}
\end{quotation}

\begin{sol}
\begin{abcd}

\item  Use the rule of seventy to decide whether Rutledge was right
  when he said the figure was ``around a million   and a half dollars''.

The rule of seventy tells me that seven percent interest doubles
a debt in ten years. In twenty years it will quadruple, in
thirty it will be eight times as large. So the \$100,000 would be
\$800,000 after 30 years. It would be \$1,600,000 after 40
years. That's barely over a million and a half, so I don't think
it would be a million and a half after just 34 years.

\item Calculate the answer.

\begin{equation*}
100,000 \times 1.07^{34} = 997811.353702
\end{equation*}
%
so the \$100,000 debt would grow to just about a million dollars in 34
years.
\end{abcd}

\end{sol}


