the price per gallon of gas with a $7 car wash is $3.19 and the price without the car wash is $3.39. When is it worth it to buy the car wash? When is it worth it if the car wash costs $2?

Answer:

The price per gallon of gas with a $7 car wash is $3.19

Then if you purchase x gallons of gas and also pay for the car wash, the total cost is:

C(x) = $7 + $3.19*x

In the case that you do not pay for the car wash, the cost per gallon is $3.39

Then the cost for x gallons of gas in this case is:

K(x) = $3.39*x

When is it worth it to buy the car wash?

We need to sett the equations:

C(x) = K(x)

This means that you pay exactly the same in both cases, but in one ( C(x)) you get the car wash and in the other not.

Then we need to solve:

$7 + $3.19*x = $3.39*x

$7 = ($3.39 - $3.19)*x = $0.20*x

$7/$0.20 = x = 35

Then for 35 gallons, is worth to buy the car wash.

In the case where the car wash costs $2, then the equation C(x) becomes:

C(x) = $2 + $3.19*x

Then if we solve the same equation:

C(x)  =K(x)

$2 + $3.19*x = $3.39*x

$2 = ($3.39 - $3.19)*x

$2 = $0.20*x

$2/$0.20 = x

10 = x

Then for 10 galons is whort  buy the car wash.

simplify 8x+7-x-4


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