Thermodynamics - Cooling of a liquid. The temperature of a liquid is measured
every 20 minutes and the results recorded in the table below.
\begin{tabular}{lrllllrr}
\hline Time \((\min )\) & 0 & 20 & 40 & 60 & 80 & 100 & 120 \\
Temp \(\left({ }^{\circ} \mathrm{C}\right)\) & 96 & 88 & 81 & 76 & 72 & 70 & 68
\\\
\hline
\end{tabular}
Calculate the rate of decrease of temperature. in units of \({ }^{\circ}
\mathrm{C}\) per minute:
(a) in the first 20 minutes
(b) in the first 40 minutes
(c) in the first 60 minutes
(d) in the last 60 minutes
(e) in the last 20 minutes
In each case express your answer as a fraction in its simplest form.