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.

Question

9+(−7)


(1 point)
Responses

Sebastian should have started at zero before adding –7.
Sebastian should have started at zero before adding –7. - incorrect

Sebastian should have switched the two addends and written −7+9
.
Sebastian should have switched the two addends and written negative 7 plus 9. - no response given

Sebastian should have used –9 and 7.
Sebastian should have used –9 and 7. - no response given

Sebastian should have used 0 and –9.

Answer 1

To describe Sebastian's movement correctly, let's analyze the situation step by step:

1. He starts at the lobby, which we can consider as level 0.
2. He goes up 7 floors, which can be represented as +7.
3. Then, he goes down 9 floors. The downward movement is represented as -9.

To express that movement starting from the lobby (0), we can set it up as:

\[ 0 + 7 - 9 \]

This simplifies to:

\[ 7 - 9 = -2 \]

This means he ends up at the second floor below the lobby after all movements.

Now, looking closely at the expression 9 + (−7):

• The 9 represents moving down, but if we think of it in terms of a starting point, it doesn't correctly represent the scenario of starting from the lobby and moving up and then down.

If we're considering the elevator rides in the context of the floors:

• He should have used +7 for going up and then -9 for going down.

Therefore, the best response from the options is:

• Sebastian should have used –9 and 7.

This option indicates the correct floors moved relative to the starting point.