paulina gets on an elevator. at the first stop, 4 people get off and 3 get on. at the second stop, 5 people get off and one gets on. at the third stop, paulina gets off. if 4 people are still in the elevator when paulina gets off, how many people were on the elevator when she got on?

Let x = number of people when she got on.
x -4+3 -5+1 -1 = 4
x -6 = 4
Solve for x to get x=10.
So there were 10 people when Paulina got on (including herself).