It\'s like this:
They\'re going to pay $30 for a meal. They get a $5 discount. If they divided this up evenly, they\'d each pay $8.33. They decided this was too messy, so they instead only took $3 of the discount. In other words, they were paying $27. At this point, however, they decided that they didn\'t want the restaurant to get the $2 because of the bad food, so instead of letting the restaurant take it, they gave it to the waiter.
In summary:
$30 price - $5 discount = 25$
$2 of the discount go to the waiter since the three people actually only take $3 of discount (to avoid messiness). The three people each pocket $1 from the discount and pay $9 dollars each (total of $27), $25 of which goes to the restaurant, $2 of which goes to the waiter. Good?

EDIT: \"food,\" not \"service\"