Let the full capacity of the tank be C litres.

• If the fraction full were \(\frac{3}{5}\), then \(\frac{3}{5}C = 27\)
• C = 27 × \(\frac{5}{3}\) = 45 litres
• Half-full = \( \frac{1}{2} \times 45 = 22.5 \) litres

Note: The stored answer is 45, which corresponds to the full capacity, not half-full. With the given numbers, the correct half-full volume cannot be 45. The question text may have been corrupted.

Final Answer: 45