Question

Sebastian was in a hotel lobby and took the elevator up 7 floors to his room. Then he took the elevator down 9 floors to the parking garage. He described his movement with the expression below. 9 + (negative 7) What is Sebastian's error?

Answer 1

Sebastian should have started at zero before adding –7.

Explanation:

nvm wrong

Answer 2

Sebastian's error = 9 + (-7)

The correct expression for Sebastian's movement = 7 + (-9)

Explanation:

Using the Lobby as a reference point

Sebastian's took 7 floors to his room

Hence, Lobby + 7 floors = Sebastian's room

Then, he took 9 floors down to the garage

Hence, Room - 9 floors = Garage

Therefore the total movement for Sebastian = Number of floors taken to his room + Number of floors taken to the garage

= 7 +(-9)

a) Sebastian's error was making the number of movements to his room negative, it is meant to be positive because he took the elevators UP

b) Sebastian's error was making the number of movements to the elevator positive, it is meant to be negative because he took the elevators DOWN to the garage

Hence, the correct expression = 7 +(-9)