The temperature at 12 noon was $ 23^{\circ} \mathrm{C} $. If the temperature decreases at the rate of $ 3^{\circ} \mathrm{C} $ per hour until midnight, find the temperature at midnight.

Given: The temperature at $12$ noon was $23^{\circ}\ C$. If the temperature decreases at the rate of $3^{\circ}\ C$ per hour until midnight.

To do: To find the temperature at midnight.

Solution:

As given, decrease in temperature $=3^{\circ}\ per\ hour$

Temperature at $12$ noon$=23^{\circ}$ 

Time $=$ from $12$ noon to mid-night$=12\ hour$

Thus, decrease in temperature in $12\ hour=12\times 3=36^{\circ}$

Therefore, temperature at mid-night$=23^{\circ}-36^{\circ}=-13^{\circ}$