Question

A certain car can travel on a highway for 350 miles on 15 gallons of gas and in a city for 280 miles on 18 gallons of gas. If the car uses twice as many gallons for city driving as for highway driving, what is the car's average number of miles per gallon? Express your answer to the nearest whole number.

Answer 1

Answer:

The car's average 18 number of miles per gallon

Step-by-step explanation:

The car has different efficiencies depending if its used on highway or city streets.

The efficiency on a highway is:

$E_h=\dfrac{350}{15}\;\text{miles/gal}=23.33\;\text{miles/gal}$

The efficiency for city driving is:

$E_c=\dfrac{280}{18}\;\text{miles/gal}=15.56\;\text{miles/gal}$

We now that the car uses twice as many gallons for city driving as for highway driving. This means that, for every gallon consumed, 2/3 are for city driving and 1/3 are for highway driving.

Then, we can calculate how many miles makes the car on average as:

$E=\dfrac{1}{3}E_h+\dfrac{2}{3}E_c\\\\\\E=\dfrac{1}{3}\cdot 23.33+\dfrac{2}{3}\cdot15.56=7.78+10.37=18.15\;\text{miles/gal}$