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

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

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

Sebastian should have used 0 and –9.

Answer 1

To analyze Sebastian's movement, he first goes up 7 floors (which we can represent as +7) and then goes down 9 floors (which we can represent as -9).

This means he can express his total movement starting from a neutral position (0) like this:

• Starting from 0, going up 7 floors can be represented as: 0 + 7
• Then, moving down 9 floors from there can be represented as: (0 + 7) - 9 or simply 7 - 9.

If we look at Sebastian's expression of 9 + (-7), it doesn't correctly represent his movements as it suggests starting from 9 floors rather than from a neutral position.

Among the responses provided, the most appropriate one is:

Sebastian should have used –9 and 7.

Because moving down 9 floors can be represented as -9 and moving up 7 floors can be represented as +7. Thus, he should consider his position more correctly reflecting the down movement first.