Elevator Integer Model

Pre-Algebra · Axiom Academy

An elevator riding past the ground floor turns every integer into a place you can stand — above is positive, below is negative, and zero is the lobby. 1. The Shaft Is a Number Line, Standing Up Stand the number line on end and it becomes an elevator shaft. The lobby is floor 0 . Floors above the street are the positive integers; the parking levels below it are the negative integers. Watch the car ride the whole shaft — every place it stops has a number you can read straight off the wall. A ride is a move, and the move has a sign. Press up one floor and the floor number grows by 1 — that's adding. Press down one floor and it shrinks by 1 — that's subtracting. Watch the car leave the lobby, climb three floors one press at a time, then ride back down through zero into the basement. The floor number rises. Up one floor is +1 ; up five floors is +5 . The floor number falls. Down one floor is -1 ; down five floors is -5 . Where you begin is the first number — it can already be negative. Start floor plus the signed move equals the floor you arrive on. start floor + signed move = end floor Here's the move from the front of the building's manual: you're on floor +3 and the elevator goes down 5 floors. Watch the car fall — it passes +2, +1, lands on the lobby at 0, then keeps going underground to −1 and stops at −2 . Crossing zero is the whole point: subtracting more than you started with drops you below the street.

This is the written version of the interactive lesson above. See the full Pre-Algebra course.