Answered

There were eighteen people seated on the roller coaster ride. For every two people seated there was one empty seat. How many empty seats are there?

Verified Answer :

9 seats were empty between the two people seated of the 18.

There is 9 empty seats because if you put it like this-

($- are people)( Empty Seat [])

$
 $ []
$
$ []
$
$ []
$
$ []
$
$ []
$
$ []
$
$ []
$
$ []
$
$ []
So if there is 2 people in each row there is one empty seat... so for every 2 people there is one empty seat. So you have 9 empty seats for the 18 people riding.