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Tracy has a cell phone plan that provides 250 free minutes each month for a flat rate of [tex]$\$[/tex] 29[tex]$. For any minutes over 250, Tracy is charged $[/tex]\[tex]$ 0.35$[/tex] per minute. Which of the following piecewise functions represents charges based on Tracy's cell phone plan?

A. [tex]f(x)=\left\{\begin{array}{ll} 29, & x \leq 250 \\ 29 + 0.35x, & x \ \textgreater \ 250 \end{array}\right\}[/tex]

B. [tex]f(x)=\left\{\begin{array}{ll} 29, & x \leq 250 \\ 29 + 0.35(x - 250), & x \ \textgreater \ 250 \end{array}\right\}[/tex]

C. [tex]f(x)=\left\{\begin{array}{ll} 29, & x \leq 250 \\ 35x, & x \ \textgreater \ 250 \end{array}\right\}[/tex]

D. [tex]f(x)=\left\{\begin{array}{ll} 29, & x \leq 250 \\ 29 + 35x, & x \ \textgreater \ 250 \end{array}\right\}[/tex]


Sagot :

To determine which piecewise function correctly represents the charges based on Tracy's cell phone plan, we need to carefully analyze each option given the details provided:

1. Understand the plan:
- Tracy pays a flat rate of \[tex]$29 for the first 250 minutes. - For any additional minutes beyond 250, Tracy is charged \$[/tex]0.35 per minute.

2. Analyze each option:

Option A:
[tex]\[ f(x) = \begin{cases} 29, & x > 250 \\ 29 + 0.35x, & x \leq 250 \end{cases} \][/tex]
- For [tex]\(x > 250\)[/tex], it states the charge remains \[tex]$29, which is incorrect because there should be an additional charge for the extra minutes. - For \(x \leq 250\), it states the charge is \(29 + 0.35x\), which means it incorrectly adds \$[/tex]0.35 per minute for all minutes, even the first 250, which are free.

Option B:
[tex]\[ f(x) = \begin{cases} 29, & x \leq 250 \\ 29 + 0.35(x-250), & x > 250 \end{cases} \][/tex]
- For [tex]\(x \leq 250\)[/tex], it correctly states the charge is a flat \[tex]$29. - For \(x > 250\), it correctly computes the charge as the flat \$[/tex]29 plus \[tex]$0.35 for each additional minute over 250. Option C: \[ f(x) = \begin{cases} 29, & x \leq 250 \\ 35x, & x > 250 \end{cases} \] - For \(x \leq 250\), it correctly states the charge is \$[/tex]29.
- For [tex]\(x > 250\)[/tex], it incorrectly states the charge is \[tex]$35 per minute for all minutes, which doesn't make sense according to the plan. Option D: \[ f(x) = \begin{cases} 29, & x \leq 250 \\ 29 + 35x, & x > 250 \end{cases} \] - For \(x \leq 250\), it correctly states the charge is \$[/tex]29.
- For [tex]\(x > 250\)[/tex], it incorrectly states the charge is \[tex]$29 plus \$[/tex]35 per minute for all minutes, which is an erroneous interpretation of the plan.

After evaluating each option:

- Option A is incorrect because it miscalculates the charges for both [tex]\(x \leq 250\)[/tex] and [tex]\(x > 250\)[/tex].
- Option C is incorrect because it applies an erroneous \[tex]$35 charge for all minutes when \(x > 250\). - Option D is incorrect because it adds an excessive \$[/tex]35 per minute charge on top of the flat \$29.

The correct representation is found in Option B, which accurately models the charges:
[tex]\[ f(x) = \begin{cases} 29, & x \leq 250 \\ 29 + 0.35(x-250), & x > 250 \end{cases} \][/tex]

Thus, Option B is the correct piecewise function representing Tracy's cell phone plan charges.