Question

You are going on a road trip over a distance of 3000 kilometers with three friends. The car consumes 6 liters of gas per 100 kilometers and gas costs $1.20 per liter.
If you want to split the cost of gas evenly between the four of you, how much should each of you chip in?

Answer 1

Let's make the rule of three: (To calculate the volume of gas spent by the distance traveled)

(volume)_____(Distance)
6 L ----------------- 100 Km
x L ----------------- 3000 Km

Directly proportional
$\frac{6}{x} = \frac{100}{3000}$
multiply cross
$100*x = 6*3000$
$100x = 18000$
$x = \frac{180\diagup\!\!\!\!0\diagup\!\!\!\!0}{1\diagup\!\!\!\!0\diagup\!\!\!\!0}$
$\boxed{x = 180\:L}$

Let's make the rule of three: (To calculate the amount of gas consumed by the volume in liters consumed).

(volume)_____(value)
1 L ----------------- $1.20
180 L ------------- $ y

Directly proportional
$\frac{1}{180} = \frac{1.20}{y}$
multiply cross
$1*y = 180*1.20$
$y = 216 \to \boxed{\ 216}$

Now divide the value between the four friends:
$\frac{216}{4} = \boxed{\ 54}$

Therefore:
$\underline{The\:gas\:cost\:evenly\:among\:the\:four\:will\:be\:\ \:54}$