To find the percentage of medium-sized jerseys, you can use the formula:
\[ \text{Percentage} = \left(\frac{\text{Number of medium-sized jerseys}}{\text{Total number of jerseys}}\right) \times 100 \]
Given that there are 6 medium-sized jerseys out of a total of 800 jerseys:
\[ \text{Percentage} = \left(\frac{6}{800}\right) \times 100 \]
Calculating this:
\[ \frac{6}{800} = 0.0075 \]
Now, multiply by 100 to convert to a percentage:
\[ 0.0075 \times 100 = 0.75 \]
Therefore, 0.75% of the jerseys are medium-sized jerseys.