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Proportional relationships in graphs

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5502347
The graph shows a proportional relationship \(y=kx\). What is the constant of proportionality \(k\)?
Figure for problem 550234

Hints

- Look for the output that corresponds to one unit of input. - The constant tells how much \(y\) changes for each \(1\) unit of \(x\). - Because the relationship is proportional, the graph value at \(x=1\) is the multiplier in \(y=kx\).

Solution

1. At \(x=1\), the graph has \(y=3\). 2. Therefore the unit rate and constant of proportionality are \(k=3\).

Answer

\(k=3\)
5519287
The graph shows the distance \(d\), in miles, traveled after \(t\) hours at a constant rate. Use the graph to find the distance traveled in \(3\) hours.
Figure for problem 551928

Hints

- Start with the given time on the horizontal axis. - Move to the plotted relationship, then read the matching value on the vertical axis. - Use the axis label to attach the correct unit to the value you read.

Solution

1. Locate \(t=3\) on the x-axis. 2. Read the y-value where the graph is above that input. 3. The graph gives \(d=6\), so the distance is \(6\,\text{miles}\).

Answer

\(6\,\text{miles}\)
5546067
The graph shows the cost \(C\), in dollars, of buying \(x\) pounds of peaches at a proportional price. Use the graph to find the cost of \(1\,\text{lb}\) of peaches. State the unit rate with units.
Figure for problem 554606

Hints

- Locate \(1\) on the horizontal axis. - Read the corresponding cost from the line. - Use the axis labels to state the unit rate with units.

Solution

1. At \(x=1\), the graph has \(C=3\). 2. Therefore, the unit rate is \(\$3\) per pound.

Answer

The unit rate is \(\$3\) per pound.
5332117
At a farmers market, the cost of potatoes is directly proportional to their weight. Use the graph to write an equation of the form \(y = kx\), where \(x\) is the weight in pounds and \(y\) is the cost in dollars.
Figure for problem 533211

Hints

- A proportional relationship has a graph that passes through the origin. - Choose a point on the line that lies at a grid intersection. - Divide cost by weight to find the unit rate \(k\).

Solution

1. A directly proportional relationship has the form \(y = kx\). 2. The point \((4, 3)\) lies on the graph, so \(4\) pounds cost \(\$3\). 3. The constant of proportionality is \(k = \frac{y}{x} = \frac{3}{4} = 0.75\). 4. Therefore, the equation is \(y = 0.75x\).

Answer

\(y = 0.75x\)
5502077
The graph shows the distance \(d\), in miles, that Maya walks after \(t\) hours at a constant pace. a) Find the constant of proportionality from the graph and explain its meaning. b) Write an equation relating \(d\) and \(t\).
Figure for problem 550207

Hints

- Look for the graph value that corresponds to one unit of time. - Use the axis labels to determine the units of the constant. - Connect the constant rate to the standard equation for a proportional relationship.

Solution

1. At \(t=1\), the graph has \(d=2.5\), so the constant of proportionality is \(2.5\) miles per hour. 2. The proportional relationship is \(d=2.5t\).

Answer

a) \(2.5\) miles per hour; Maya walks \(2.5\) miles each hour. b) \(d=2.5t\)
5502107
The graph shows the amount of water \(V\), in gallons, added to an empty tank after \(t\) minutes. The relationship is proportional. a) What point on the graph has \(t=1\)? b) Explain what that point means in this situation.
Figure for problem 550210

Hints

- Locate the input value of one on the horizontal axis. - Read the matching output from the line. - Interpret both coordinates using the axis units.

Solution

1. At \(t=1\), the graph gives \(V=6\), so the point is \((1,6)\). 2. The point means that after \(1\,\text{minute}\), \(6\,\text{gallons}\) have been added; equivalently, the constant of proportionality is \(6\,\text{gallons per minute}\).

Answer

a) \((1,6)\) b) It means the tank receives \(6\,\text{gallons}\) in \(1\,\text{minute}\), so the rate is \(6\,\text{gallons per minute}\).
5502337
The graph shows the proportional relationship between the number of pounds of apples \(x\) and their cost \(C\), in dollars. Point \(P\) is marked on the graph. a) What does point \(P\) mean in this situation? b) What does the point \((1,2.5)\) mean? c) Explain why the graph includes \((0,0)\).
Figure for problem 550233

Hints

- Match each coordinate with the variable on its axis. - Think about what an x-coordinate of \(1\) means in context. - Interpret the origin using the real quantities, not only the graph rule.

Solution

1. Point \(P=(4,10)\) means \(4\,\text{pounds}\) of apples cost \(\$10\). 2. The point \((1,2.5)\) means \(1\,\text{pound}\) costs \(\$2.50\); this is the unit rate. 3. The point \((0,0)\) means buying \(0\,\text{pounds}\) costs \(\$0\), which is required for this proportional relationship.

Answer

a) \(4\,\text{pounds}\) of apples cost \(\$10\). b) \(1\,\text{pound}\) costs \(\$2.50\). c) \(0\,\text{pounds}\) costs \(\$0\), so the graph passes through the origin.
5545297
A tank starts empty and fills continuously at \(4\) gallons per minute for the first \(5\) minutes. The graph below is unfinished. a) Give the endpoints of the line segment that must be added to complete the graph through \(t=5\) minutes. b) Explain why the missing part should be a connected line segment rather than only another isolated point.
Figure for problem 554529

Hints

- Inspect where the segment already drawn on the graph ends. - Identify the later marked point that the completed graph must reach. - Decide whether every time between those two x-values has a meaningful volume.

Solution

1. The unfinished graph already contains the segment ending at \((2,8)\) and shows the later endpoint \((5,20)\). 2. Therefore, the missing segment must run from \((2,8)\) to \((5,20)\). 3. Filling occurs continuously, so every time between \(2\) and \(5\) minutes has a corresponding volume. The graph needs the entire connecting segment, not only an isolated point at \((5,20)\).

Answer

a) Add the segment from \((2,8)\) to \((5,20)\). b) Use a connected line segment because time and water volume vary continuously during filling.
5545307
Cyclists P and Q start at the same location and each travel at a constant speed. Their distance-time graphs are shown. a) Find the speed of each cyclist in miles per hour. b) Which cyclist is faster, and by how many miles per hour? c) For each graph, explain how the point with x-coordinate \(1\) shows the constant of proportionality.
Figure for problem 554530

Hints

- Compare how much distance each graph shows after the same amount of time. - On a proportional graph, the y-value at an x-value of \(1\) has a special interpretation. - Use the difference between the two unit rates for part b).

Solution

1. Both graphs pass through the origin, so each speed is the slope \(\frac{d}{t}\). 2. Graph p passes through \((1,4)\), so Cyclist P travels at \(4\) miles per hour. 3. Graph q passes through \((1,6)\), so Cyclist Q travels at \(6\) miles per hour. 4. Cyclist Q is faster by \(6-4=2\) miles per hour. 5. In a proportional graph \(d=kt\), the point \((1,k)\) has y-coordinate equal to the unit rate. Here those y-coordinates are \(4\) and \(6\).

Answer

a) Cyclist P: \(4\) miles per hour; Cyclist Q: \(6\) miles per hour b) Cyclist Q is faster by \(2\) miles per hour. c) The points \((1,4)\) and \((1,6)\) show the unit rates because the y-coordinate at \(t=1\) equals \(k\).
5546057
An arcade charges \(\$3\) per game with no entrance fee. The number of games \(g\) must be a whole number from \(0\) through \(5\), and the cost is \(C=3g\). The graph below is unfinished. a) Which two ordered pairs must be added to the graph so that every allowed game count is represented? b) Should any of the plotted points be connected by line segments? Explain.
Figure for problem 554605

Hints

- Inspect which allowed whole-number game counts are already represented on the graph. - Use the equation only for the allowed inputs that are missing from the graph. - Think about whether a point between two whole-number game counts would represent a possible purchase.

Solution

1. The graph already shows the allowed inputs \(g=0\), \(1\), \(3\), and \(5\), so the missing whole-number inputs are \(2\) and \(4\). 2. Using \(C=3g\), the missing points are \((2,6)\) and \((4,12)\). 3. The points should not be connected because the number of games is discrete; values such as \(2.5\) games are not possible in this situation.

Answer

a) \((2,6)\) and \((4,12)\) b) No. Keep the points isolated because the number of games can only be a whole number.
5119087
The graph shows Sofia's distance during the first \(5\) hours of a bicycle ride. a) Use the graph to determine Sofia's constant speed in miles per hour. State a point from the graph that supports your answer. b) Make a table for the relationship between time, in hours, and distance, in miles, for \(1\), \(2\), \(3\), \(4\), and \(5\) hours. c) Why does it make sense in this situation for the graph to be a connected line instead of isolated points? d) Use the graph to find the distance after \(150\) minutes, then verify the value using the speed from part a).
Figure for problem 511908

Hints

- Read a convenient point on the line and compare its distance coordinate with its time coordinate. - Use the rate you found from the graph to build the whole-hour table. - Think about whether Sofia also travels during parts of an hour. - Convert \(150\) minutes to hours and locate that time directly on the graph before checking by calculation.

Solution

1. The graph contains points such as \((1,12)\) and \((2,24)\). The ratio of distance to time is \(12\), so Sofia's speed is \(12\,\text{mi/h}\). 2. Use the rate \(12\,\text{mi/h}\) to complete the table. <table><tr><td>Time</td><td>\(1\,\text{h}\)</td><td>\(2\,\text{h}\)</td><td>\(3\,\text{h}\)</td><td>\(4\,\text{h}\)</td><td>\(5\,\text{h}\)</td></tr><tr><td>Distance</td><td>\(12\,\text{mi}\)</td><td>\(24\,\text{mi}\)</td><td>\(36\,\text{mi}\)</td><td>\(48\,\text{mi}\)</td><td>\(60\,\text{mi}\)</td></tr></table> 3. A connected line makes sense because time and distance vary continuously during the ride, including between whole-hour times. 4. Since \(150\) minutes is \(2.5\) hours, the graph gives \(30\) miles at \(t=2.5\). The calculation \(12\cdot2.5=30\) verifies the graph reading.

Answer

a) \(12\,\text{mi/h}\); for example, the graph contains \((1,12)\). b) <table><tr><td>Time</td><td>\(1\,\text{h}\)</td><td>\(2\,\text{h}\)</td><td>\(3\,\text{h}\)</td><td>\(4\,\text{h}\)</td><td>\(5\,\text{h}\)</td></tr><tr><td>Distance</td><td>\(12\,\text{mi}\)</td><td>\(24\,\text{mi}\)</td><td>\(36\,\text{mi}\)</td><td>\(48\,\text{mi}\)</td><td>\(60\,\text{mi}\)</td></tr></table> c) A connected line makes sense because Sofia travels continuously between the listed times. d) \(30\,\text{mi}\); the graph shows \((2.5,30)\), and \(12\cdot2.5=30\).
5119107
The graph shows the amount of ink used for selected whole-page counts by a printer. Assume the relationship is proportional. a) Use the graph to find the ink used per page. State which plotted point you used. b) The graph shows selected whole-page counts and the corresponding ink used. Describe two visual features of the plotted points that are consistent with a proportional relationship. c) A new ink cartridge contains \(40\,\text{mL}\) of ink. Use the graph to find how many full pages it can print, then verify by calculation using your unit rate from part a).
Figure for problem 511910

Hints

- Choose a plotted point with nonzero coordinates and use it to determine ink per page. - Check where the plotted pattern begins and whether all plotted points align. - Decide whether the number of fully printed pages can take non-whole-number values. - For the cartridge question, first read the page count paired with \(40\,\text{mL}\) from the graph, then check it using your rate.

Solution

1. One convenient plotted point is \((400,10)\). The unit rate is \(10\div400=0.025\,\text{mL}\) per page. 2. The plotted points include the origin and lie on one straight-line pattern. Those features are consistent with a proportional relationship. The points are not connected because page count is discrete. 3. On the graph, the plotted point with ink use \(40\,\text{mL}\) has page count \(1600\). 4. The calculation \(40\div0.025=1600\) verifies the graph reading.

Answer

a) \(0.025\,\text{mL}\) per page; for example, using \((400,10)\), \(10\div400=0.025\). b) The plotted points include the origin and lie on one straight-line pattern. They remain isolated because the number of fully printed pages is discrete. c) \(1600\) pages. The graph shows \((1600,40)\), and \(40\div0.025=1600\).
5502097
The table shows a proportional relationship. Which graph, a), b), or c), represents the same relationship? Explain how you know. <table><tr><td>\(x\)</td><td>\(1\)</td><td>\(2\)</td><td>\(4\)</td></tr><tr><td>\(y\)</td><td>\(1.5\)</td><td>\(3\)</td><td>\(6\)</td></tr></table>
Figure for problem 550209

Hints

- Find a feature of the table that stays constant from column to column. - Use one or more table points to compare with the graphs. - Check both the rate and whether the graph has the required proportional form.

Solution

1. The table has constant ratio \(\frac{y}{x}=1.5\). 2. Graph a) represents \(y=1.5x\) and contains the table points, including \((4,6)\). 3. Graph b) has a larger constant of proportionality, and graph c) does not pass through the origin.

Answer

Graph a) represents the table.
5502117
The graph shows the total cost \(C\), in dollars, for a whole-number quantity \(n\) of museum tickets. The relationship is proportional. a) Use the graph to find how many tickets cost \(\$35\). b) Write an equation for \(C\) in terms of \(n\) and use it to confirm your answer.
Figure for problem 550211

Hints

- Start with the given cost on the vertical axis and locate the plotted point at that height. - Use the plotted point for one ticket to identify the cost per ticket. - Remember that ticket counts are whole numbers, so the graph uses isolated points.

Solution

1. The plotted point with \(C=35\) has \(n=5\). 2. The points show a unit cost of \(7\) dollars per ticket, so \(C=7n\) for whole-number ticket counts. 3. Substituting \(C=35\) gives \(35=7n\), so \(n=5\).

Answer

a) \(5\) tickets b) \(C=7n\) for whole-number \(n\), and \(35=7\cdot5\).

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