To find out how many gallons of milk Marie drank each day, we can divide the total amount of milk by the number of days it lasted.
Marie bought \( \frac{1}{2} \) gallon of milk and finished it in 6 days. To find out how much she drank each day, we perform the following calculation:
\[ \text{Amount of milk per day} = \frac{\text{Total milk}}{\text{Number of days}} = \frac{1/2}{6} \]
To divide by 6, we can multiply \( \frac{1}{2} \) by the reciprocal of 6, which is \( \frac{1}{6} \):
\[ \frac{1/2}{6} = \frac{1}{2} \times \frac{1}{6} = \frac{1}{12} \]
Therefore, Marie drank \( \frac{1}{12} \) of a gallon of milk each day.
So the answer is: StartFraction 1 Over 12 EndFraction of a gallon.