Question

When going more than 38 miles per hour, the gas mileage of a certain car fits the model y = 43.81 - .395x where x is the speed of the car in miles per hour and y is the miles per gallon of gasoline. Based on this model, at what speed will the car average 15 miles per gallon? (Round to nearest whole number.)

Answer 1

d. 73

The car will average 15 miles per gallon at the speed 73 miles per hour

Explanation:

Your equation is: y = 43.81 - 0.395x

We need to solve for x if y = 15

So plug 15 into your equation: 15 = 43.81 - 0.395x

Then rearrange your equation to get the variable by itself and change the sign: 0.395x = 43.81 - 15

Subtract 43.81 - 15 = 28.81

0.395x = 28.81

Then divide both sides of the equation by 0.395

0.395x/0.395 = 28.81/0.395

x = 72.9367088608

Then (Round to nearest whole number.)

Giving you your solution of 73

To Conclude:

The car will average 15 miles per gallon at the speed 73 miles per hour

Answer 2

15= 43.81-.395x
move the 43.81 to the other side by subtracting it on both sides.
-28.81=-.395x
divide -28.81 by -.395 and get x
x=72.9367= 73 miles per hour to get 15 miles per gallon