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)



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(1 point)
Responses

Sebastian should have used 0 and –9.
Sebastian should have used 0 and –9.

Sebastian should have switched the two addends and written −7+9
.
Sebastian should have switched the two addends and written negative 7 plus 9.

Sebastian should have used –9 and 7.
Sebastian should have used –9 and 7.

Sebastian should have started at zero before adding –7.

Answer 1

To correctly describe Sebastian's movement using integers, we should analyze his actions:

1. Starting point: Let's assume he starts at floor 0 (the lobby).
2. Going up 7 floors: This can be represented as +7.
3. Going down 9 floors: This is represented as -9.

So, his total movement can be expressed as:

• Starting at 0, he goes up 7 floors (which can be written as 0 + 7 or just +7).
• Then, he goes down 9 floors, which can be represented as 7 - 9 (or +7 + (-9)).

This leads us to the expression: \[ 7 - 9 \] or, equivalently, \[ -9 + 7 \]

Given the options:

• Sebastian should have switched the two addends and written −7+9. This is incorrect because -7 doesn't represent his upward movement.

• Sebastian should have used 0 and –9. This also doesn't accurately reflect the problem; there needs to be a representation of him going up 7 first.

• Sebastian should have used –9 and 7. This is incorrect in its order since he starts by going up.

• Sebastian should have started at zero before adding –7. This option makes sense, but it doesn't fully capture the downward movement.

Based on the logical breakdown, the best representation is negative 9 plus 7. Therefore, your best response would be:

Sebastian should have switched the two addends and written −7+9.

So, go with that option, as it captures the movement correctly, even if the negatives and positives are not in conventional order.