Save Gas Money with Math

Today's question is very simple, but it will show you have to save money on gas very easily. Watch and learn:

Mary needs to refuel her car with 60 liters of gasoline and get back home. She has two choices: drive to a gas station 20 km away from her house which charges $1.16/liter or drive to a gas station adjacent to her house which charges $1.24/liter. Mary's car's mileage is 10 km/liter. Which is cheaper for Mary?

This question does not require complicated calculations, so let's do them:
The price for Mary on the close station: 60 * $1.24 = $74.4
The price for Mary on the far station: 60 * $1.16 = $69.6

That's quite a difference. Now we only have to see how much it costs mary to drive back and forth:
She can do 10 km/liter, so she spends a total of 40 / 10 = 4 liters to drive to the gas station and back.

Now let's find how much this trip costs her (using the cheap gas price, of course):
4 * $1.16 = $4.64
$69.6 + $4.64 = $74.24

In total, Mary saves 16¢ per 60 liters, or 0.267¢ per liter (1.008¢ per gallon). Not worth the trouble. If her mileage was double, 20 km/liter, she would've saved about $2 for these 60 liters, which is about 15¢ per gallon. Now that's a difference.

Yours,
Nadav

nadavs