Question

You drive an average of 450 miles per week in a car that gets 22 miles per gallon. with gasoline priced at $3.50 per gallon on average, approximately how much would you save each year on gas if you instead had a car that got 40 miles per gallon?

Answer 1

First we have to compute how much we spend money each year. 
Compute like this:
$\frac{450}{22}=20.45$ is the number of gallons consumed each week. 
In one year there is 48 weeks. 
Then $20.45\times48=981.6$ is the number of gallons a year. 
Now compute the price: 
$3.5\times981.6=\ 3435,6$
We do the same process with a car consuming 40 miles per gallon. 
tex] \frac{450}{40}=11.25 [/tex] gallon consumed per week. 
 $11.25\times48=540$  gallons consumed per year. 
$3.5\times540=\ 1890$ is the amount paid each year in gallons. 
So we are saving the following amount:
$\ 3435,6-\ 1890=\ 1545$