Answer: The net change would be -2.
Step-by-step explanation: The upward change of elevator is represented by positive sign while the downward change represented by negative sign.
Given, First the elevator goes up 15 floors, change = + 15, Then it goes 9 floors down, change = -9, Then it goes 11 floors up,Change = + 11, Finally, it goes 19 floor down, Change = - 19 So, the net change = sum of total changes = 15 - 9 + 11 - 19 = -2
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