High School

A scuba diver is at an elevation of -25 feet. She starts moving at a rate of -10 feet per minute. Which inequality represents how long it will take the diver to reach an elevation deeper than -220 feet?

A. [tex]-10x - 25 \leq -220[/tex]
B. [tex]-10x - 25 \geq -220[/tex]
C. [tex]-10x - 25 \ \textless \ -220[/tex]
D. [tex]-10x - 25 \ \textgreater \ -220[/tex]

Answer :

We start by expressing the diver’s elevation after [tex]$x$[/tex] minutes. Since she begins at an elevation of [tex]$-25$[/tex] feet and she descends at [tex]$10$[/tex] feet per minute (note the descent means the rate is added as [tex]$-10$[/tex]), her elevation after [tex]$x$[/tex] minutes can be written as:

[tex]$$-25 - 10x.$$[/tex]

The condition “deeper than [tex]$-220$[/tex] feet” means that her elevation is less than [tex]$-220$[/tex] feet. This gives us the inequality:

[tex]$$-25 - 10x < -220.$$[/tex]

Now, let’s solve this inequality step by step:

1. Add 25 to both sides:

[tex]$$-25 - 10x + 25 < -220 + 25$$[/tex]
[tex]$$-10x < -195.$$[/tex]

2. Divide both sides by [tex]$-10$[/tex]:

When dividing by a negative number, the inequality sign must be reversed:

[tex]$$x > \frac{-195}{-10}.$$[/tex]

Simplifying the division, we get:

[tex]$$x > 19.5.$$[/tex]

So, it will take more than [tex]$19.5$[/tex] minutes for the diver to reach an elevation deeper than [tex]$-220$[/tex] feet.

The inequality that correctly represents the scenario before solving for [tex]$x$[/tex] is:

[tex]$$-25 - 10x < -220.$$[/tex]

This corresponds to option C.