Math Problem Statement

Naoya read a book cover to cover in a single session, at a rate of [55] pages per hour. After [4] hours, he had [350] pages left to read. Let [y] represent the number of pages left to read after [x] hours. Which of the following could be the graph of the relationship?

Solution

Let's break down the problem:

Naoya reads at a rate of 55 pages per hour. After 4 hours, he has 350 pages left. This means that in those 4 hours, he has read:

55pages/hour×4hours=220pages.55 \, \text{pages/hour} \times 4 \, \text{hours} = 220 \, \text{pages}.

So, the total number of pages in the book is:

Total pages=220pages read+350pages left=570pages.\text{Total pages} = 220 \, \text{pages read} + 350 \, \text{pages left} = 570 \, \text{pages}.

Now, we need to express the relationship between the number of hours passed (xx) and the number of pages left to read (yy).

After xx hours, the number of pages left to read can be calculated as:

y=57055x.y = 570 - 55x.

This equation represents a linear relationship because Naoya reads a fixed number of pages per hour, which results in a straight-line graph where the slope is 55-55 and the y-intercept is 570.

Key features of the graph:

  • Slope: Since Naoya reads 55 pages per hour, the slope is 55-55 (negative because the number of pages left decreases over time).
  • Y-intercept: The y-intercept is 570, which is the total number of pages in the book when x=0x = 0 (before Naoya starts reading).
  • Downward sloping: The graph should show a line that slopes downward because the number of pages left decreases over time.

Conclusion:

The correct graph should be a straight line starting at 570 on the y-axis (total pages) and sloping downward at a rate of 55 pages per hour.


Would you like more details on how to interpret or graph linear equations? Here are some related questions for further exploration:

  1. How can we use the equation y=57055xy = 570 - 55x to predict how many pages are left after 6 hours?
  2. How would the graph change if Naoya read at a rate of 60 pages per hour?
  3. How can you calculate the y-intercept of a linear equation from a real-world scenario?
  4. What is the relationship between the slope of a graph and the rate of change in real-world problems?
  5. How do you convert this word problem into a different type of graph, such as a bar chart?

Tip: When interpreting word problems, always identify key details like rate of change, total amount, and how they relate to each other to form an equation.

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Math Problem Analysis

Mathematical Concepts

Linear Equations
Rate of Change
Graphing Linear Functions

Formulas

y = y0 - rx (linear equation form)
y = 570 - 55x

Theorems

Slope-Intercept Form Theorem
Linear Function Properties

Suitable Grade Level

Grades 8-10