The equation d= -6t + 10 represents the distance d, in miles, Ralph walks from the library to his house in t hours. His sister, Joan, leaves the library right after Ralph. She rides her bicycle from the library to their house at a constant rate. The equation d = 14t represents Joan's bicycle ride where d, is the distance, in miles, and t is the time, in hours.

After how many miles will Joan meet Ralph walking to their house?
A. 2.5 miles
B. 7 miles
C. 18 miles
D. 28 miles

Answer :

Space

Answer:

B. 7 miles

General Formulas and Concepts:
Algebra I

Equality Properties

  • Multiplication Property of Equality
  • Division Property of Equality
  • Addition Property of Equality
  • Subtraction Property of Equality

Terms/Coefficients

Functions

  • Function Notation

Systems of Linear Equations

  • Solving methods: Substitution/Elimination

Step-by-step explanation:

Step 1: Define

Identify given.

[Ralph's Walking Distance Function]: d = -6t + 10

[Joan's Bicycle Distance Function]: d = 14t

Step 2: Find Meeting Point

To find where Joan and Ralph will meet, we need to find where they intersect. Therefore, we need to find the time which they both meet up at. To do this, we can use the process of substitution to find our value of t:

  1. [Equation 1] Substitute in d:
    [tex]\displaystyle\begin{aligned}d = -6t + 10 & \rightarrow 14t = -6t + 10\end{aligned}[/tex]

From here, we can simply use techniques listed under "Algebra I" to solve for t:

[tex]\displaystyle\begin{aligned}14t & = -6t + 10 \\20t & = 10 \\t & = \boxed{ \frac{1}{2} } \\\end{aligned}[/tex]

∴ both Joan and Ralph will meet up in half an hour, or 0.5 hours.

Step 3: Find Mileage

To find how many miles they will meet up at, we substitute the number of hours elapsed (found in Step 2) and substitute it into any of the equations given:

[tex]\displaystyle\begin{aligned}d & = 14t \\& = 14 \bigg( \frac{1}{2} \bigg) \\& = \boxed{7} \\\end{aligned}[/tex]

∴ Joan will meet Ralph after 7 miles.

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Topic: Algebra I

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