The price of gas is advertised as $3.39 9/10 per gallon. To convert this to a decimal:
- The "3.39" represents 3 dollars and 39 cents.
- The "9/10" indicates that there is an additional 0.9 cents.
Thus, the decimal representation of the price is:
\[ 3.39 + 0.09 = 3.399 \]
Therefore, the price of a gallon of gas strictly as a decimal is 3.399.