On Wednesday, Marvin used 13 bags of hot dog buns.
On Thursday, he used half as many hot dog buns as on Wednesday. To find out how many bags he used on Thursday, we can calculate:
\[ \text{Bags used on Thursday} = \frac{1}{2} \times \text{Bags used on Wednesday} \] \[ \text{Bags used on Thursday} = \frac{1}{2} \times 13 = \frac{13}{2} \]
The fraction \(\frac{13}{2}\) can also be expressed as a mixed number:
\[ \frac{13}{2} = 6 \frac{1}{2} \]
Thus, Marvin used \(\frac{13}{2}\) bags of hot dog buns on Thursday, which is also equal to \(6 \frac{1}{2}\) bags.
The final answer is:
\(\frac{13}{2}\) or \(6 \frac{1}{2}\).