### Home > CC1 > Chapter 7 > Lesson 7.3.4 > Problem7-123

7-123.

ELEVATOR CHALLENGE

Juan got on an elevator at the middle floor of a building, went up $4$ floors, down $3$ floors, up $1$ floor, and down $9$ floors, where he left the elevator on the ground floor. Homework Help ✎

1. How many floors are in the building?

First, draw a vertical number line and pick a tick mark to represent the middle floor.

Then trace his path, starting at the middle floor and move $4$ floors up.

Then move $3$ floors down.

Next, move $1$ floor up.

Last, move $9$ floors down to the ground floor.

If you stop on the first floor and there are seven floors below the middle floor, there should be $7$ floors above. How many floors are there?

2. Explain how you found the number of floors.

Did you work backwards?
Or did you set up a number line?