Question

Carole's car averages 13.2 mi/gal in city driving and 25.3 mi/gal in highway driving. If she drove a total of 396.0 mi on 19 gal of gas, how many of the gallons (to the nearest gallon) were used for city driving?

Answer 1

7 gallons were used for city driving.

Explanation:

I am going to solve this question by a system of equations.

I am going to say that:

x is the number of gallons driven in the city.

y is the number of gallons driven in the highway.

19 gal of gas

This means that
`x + y = 19`

Carole's car averages 13.2 mi/gal in city driving and 25.3 mi/gal in highway driving. If she drove a total of 396.0 mi.

This means that
`13.2x + 25.3y = 396`

How many of the gallons (to the nearest gallon) were used for city driving?

This is x

From the first equation, i will have

`y = 19 - x`

Replacing in the second equation

`13.2x + 25.3y = 396`

`13.2x + 25.3(19 - x) = 396`

`13.2x - 25.3x = 396 - 480,7`

`12.1x = 84.7`

`x = (84.7)/(12.1)`

`x = 7`

7 gallons were used for city driving.