A car travels 250 miles using 10 gallons of gas, then travels 180 miles using 6 gallons. What is the car's combined average fuel…

Combined fuel efficiency is total miles divided by total gallons, not the average of the two rates. The total distance is $250+180=430$ miles and the total fuel is $10+6=16$ gallons, so the efficiency is $\frac{430}{16}=26.875$ miles per gallon, choice G. The first leg gets $25$ mpg and the second gets $30$ mpg, and more of the fuel was used on the slower first leg, so the overall figure must be closer to $25$ than to $30$. Choice H ($27.5$) averages the two rates, $\frac{25+30}{2}$, which weights both legs equally. Choice F ($25.0$) is the first leg alone, and choice J ($30.0$) is the second leg alone.