The Fahrenheit temperature ($F$) is related to the Celsius temperature ($C$) by $F = \tfrac{9}{5} \cdot C + 32$. What is the temperature in Fahrenheit degrees that is one-ﬁfth as large if measured in Celsius degrees?
1. We start with the given relationship between Fahrenheit temperature \( F \) and Celsius temperature \( C \):
   \[
   F = \frac{9}{5} \cdot C + 32
   \]

2. We need to find the temperature in Fahrenheit degrees that is one-fifth as large if measured in Celsius degrees. This means we need to find \( F \) such that:
   \[
   F = \frac{1}{5} C
   \]

3. Substitute \( F = \frac{1}{5} C \) into the original equation:
   \[
   \frac{1}{5} C = \frac{9}{5} \cdot C + 32
   \]

4. To eliminate the fractions, multiply every term by 5:
   \[
   C = 9C + 160
   \]

5. Rearrange the equation to isolate \( C \):
   \[
   C - 9C = 160
   \]
   \[
   -8C = 160
   \]

6. Solve for \( C \):
   \[
   C = \frac{160}{-8}
   \]
   \[
   C = -20
   \]

7. Now, substitute \( C = -20 \) back into the equation \( F = \frac{1}{5} C \) to find \( F \):
   \[
   F = \frac{1}{5} \cdot (-20)
   \]
   \[
   F = -4
   \]

The final answer is \( \boxed{ F = -4 } \)