When carpooling with a third person, the cost savings for each person can be calculated by dividing the total cost of the tank of gas by the number of people sharing it.
For example, let's say the total cost of filling up the tank is $60, and with three people sharing it, each person would pay:
$60 ÷ 3 people = $20 per person
If you and your friend were initially planning to split the cost between the two of you, you would each save:
Initial cost per person = $60 ÷ 2 people = $30 per person
Cost savings per person by adding a third person = $30 - $20 = $10
Therefore, you and your friend would each save $10 by having a third person join the carpool and share the tank of gas.
