### Home > MC1 > Chapter 4 > Lesson 4.1.2 > Problem 4-18

ELEVATOR CHALLENGE

Juan got on an elevator at the middle floor of a building, went up

How many floors are in the building?

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

**A vertical number line with the middle tick mark, labeled, middle floor.**Then trace his path, starting at the middle floor and move

floors up. **Movement of 4 up, from the middle floor.**Then move

floors down. **Movement of 3 down, from the last position.**Next, move

floor up. **Movement of 1 up, from the last position.**Last, move

floors down to the ground floor. **Movement of 9 down, from the last position.**If you stop on the first floor and there are seven floors below the middle floor, there should be

floors above. How many floors are there? **Numbers, 1 to 7, are labeled on each tick mark, starting with 1 from the last position.**Explain how you found the number of floors.

Did you work backwards?

Or did you set up a number line?