Question

Sean is filling his truck with gasoline. He knows the total cost, C, will be proportional to the
number of gallons of gasoline, g, that he puts into the gas tank. After putting 8.5 gallons in
.
the tank, the cost is $23.63.
(a) Find the ratio of the cost to the gallons as
(b) What is the real world meaning of your
a unit rate. Show the division as a fraction answer in (a)?
and then state the answer with appropriate
units.
(c) If c is the cost and g is the number of
gallons bought, write a proportion
involving c and g and then solve it for c.
(d) If Sean puts 17 gallons of gasoline into
his truck, what is his cost? Justify.

Answer 1

Part (a)

Divide the total cost over the number of gallons to get the unit cost

(23.63)/(8.5) = 2.78

Answer:  2.78

=======================================================

Part (b)

The result of the previous part indicates the gas costs $2.78 per gallon.

=======================================================

Part (c)

c = cost in dollars

g = number of gallons bought

cost/gallons = cost/gallons

c/g = (23.78)/(8.5)

c/g = 2.78

c = 2.78g

This fits with what part (b) mentioned. The 2.78g means "2.78 times g".

Answer:  c = 2.78g

=======================================================

Part (d)

Plug g = 17 into the equation found in part (c)

c = 2.78g

c = 2.78*17

c = 47.26

Answer:  $47.26