There is a relationship between how much gas your car consumes and how fast you drive. It is a curve and the peak is around 55 mph. When you are going too fast or too slow, you use more gas. The table below shows the speed vs. the gas mileage for cars.

EPA data: Gas Mileage vs. Speed

 Model Speed = 40 MPH Speed = 50 MPH Speed = 60 MPH Gas Mileage (mpg) Gas Mileage (mpg) Gas Mileage (mpg) Sub-Compact 35 36 29 Compact 28 30 27 Midsize 21 22 20 Van 15 17 13 Luxury 13 14 12

Mary is driving a van with a 15 gallon tank in a  rural area. The closest gas station is 125 miles away. She has half a tank of gas and she is traveling at 60 mph. Will she have enough gas to get to the next gas station? Can she get there if she slowed down to 50? 40?

If she drives at 60 mph:

7.5 gallons(half tank) ´  13 mpg (table above at 60 mph) = 97.5 miles

Not enough gas to reach the next gas station.

If she drives at 50 mph:

7.5 gallons ´ 17 (table above at 50 mph) = 127.5 miles

Barely enough gas to reach the next gas station.

If she drives at 40 mph:

7.5 gallons ´ 15 (table above at 40 mph) = 112.5 miles

Not enough gas to reach the next gas station.

Josh's dad is driving their Ford mid-size car at 40 mph in the desert. The road sign shows that the next gas station  is 100 miles away. They have half a tank of gas in their 20-gallon tank. Will they reach the next gas station?

yes