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7.02 Linear functions in context

Worksheet
Linear graphical models
1

The graph shows the conversion between temperatures in Celsius and Fahrenheit. Note that 0 \degree \text{C} is 32 \degree \text{F}.

a

Use the graph to convert 10 \degree \text{C} into \degree \text{F}.

b

Calculate the gradient of the line as a decimal number.

c

For every increase by 1 \degree \text{C}, by how much does the Fahrenheit temperature increase?

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35
\degree \text{C}
10
20
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80
90
\degree \text{F}
2

The graph shows the conversion between Country A and Country B's currency:

a

Use the graph to convert 8 of currency A to currency B.

b

Use the graph to convert 2 of currency B to currency A.

c

Calculate the gradient of the line.

d

Hence state the exchange rate to convert currency B to currency A.

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\text{B}
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\text{A}
3

Consider the conversions graph for miles and kilometres:

a

If a car is driving 32\text{ km/hour} in a school zone, at what speed are they travelling in miles/hour?

b

Calculate the conversion rate to change \text{km/hour} to \text{miles/h}.

c

Calculate the gradient of the line.

d

A road sign states the speed limit to be 128 kilometres per hour. What is this speed limit in miles per hour?

e

What does the gradient represent in this situation?

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32
\text{Kilometres}
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\text{Miles}
4

The graph shows the amount of water remaining in a bucket that was initially full before a hole was made in it's side.

a

Find the gradient of the line.

b

State the y-intercept.

c

Hence write an equation to represent the amount of water remaining in the bucket, y, as a function of time, x.

d

Find the amount of water remaining in the bucket after 54 minutes.

e

Explain the meaning of the gradient in this context.

f

What does the y-intercept represent in this context?

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\text{Time (mins)}
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\text{Water (L)}
5

Valentina left for a road trip at midday and travels at a constant average speed. The graph shows the total distance travelled (in kilometres), t hours after midday.

Let the horizontal axis represent the time in hours and the vertical axis represent the distance travelled in kilometres.

a

State the gradient of the line.

b

What does the gradient of the line represent in this context?

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t
115
230
345
460
575
\text{Distance (km)}
6

Consider the graph which shows the cost of a consultation with a medical specialist for a student or an adult, according to the length of the consultation:

a

Find the cost for an adult consultation of 10 minutes.

b

Find the cost for a student consultation of 10 minutes.

c
Calculate the hourly rate for an adult.
d
Calculate the hourly rate for a student.
e

Calculate the discount for the hourly rate of a student consultation.

f

Determine the percentage discount for the hourly rate of a student consultation.

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\text{Minutes}
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\text{Cost}(\$)
7

The graph shows the temperature of a room (in degrees Celcius) against the time since the heater has been turned on (in minutes).

a

Find the gradient of the function.

b

State the y-intercept.

c

Hence write an equation to represent the temperature of the room, y, as a function of time, x.

d

Find the temperature of the room after the heater has been turned on for 30 minutes.

e

What does the gradient represent in this context?

f

What does the y-intercept represent in this context?

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\text{Time (mins)}
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\text{Temp } (\degree C)
8

The graph shows the temperature of a room after the heater has been turned on.

a

State the gradient of the line.

b

State the y-intercept.

c

Write an equation to represent the temperature of the room, y, as a function of time, t.

d

Explain the meaning of the gradient in this context.

e

Explain the meaning of the y-intercept in this context.

f

Find the temperature of the room after the heater has been turned on for 40 minutes.

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t\text{ (mins)}
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\text{Temp (}\degree \text{C)}
9

A carpenter charges a callout fee of \$150 plus \$45 per hour.

a

Write a linear equation to represent the total amount charged, y, by the carpenter as a function of the number of hours worked, x.

b

State the gradient of the linear function.

c

Explain the meaning of the gradient in this context.

d

State the value of the y-intercept.

e

Explain the meaning of the y-intercept in this context.

f

Find the total amount charged by the carpenter for 6 hours of work.

10

Mohamad is taking his new Subaru out for a drive. He had only driven 50 kilometres in it before and is now driving it down the highway at 75\text{ km/h} .

a

Write an equation to represent the total distance, y, that Mohamad had driven in his Subaru as a function of the number of hours, x.

b

State the gradient of the function.

c

Describe what the gradient of the line represents in context.

d

Find of the y-intercept.

e

Describe what the y-intercept represents in context.

f

Find the total distance Mohamad will have driven in his Subaru if his current drive begins at 5:10 pm and finishes at 7:25 pm.

11

Mario is running a 100 \text{ km} ultramarathon at an average speed of 9 \text{ km/h}.

a

Write an equation to represent the distance Mario has left to run, y, as a function of the number of hours since the start, x.

b

State the gradient of the function.

c

Describe what the gradient of the line represents in context.

d

Find the y-intercept.

e

Describe what the y-intercept represents in context.

f

Find the distance Mario will have left to run after 4.5 hours.

12

A particular restaurant has a fixed weekly cost of \$1300 and receives an average of \$16 from each customer.

a

Write an equation to represent the net profit, y, of the restaurant for the week as a function of the number of customers, x.

b

Find the gradient of the function.

c

Describe what the gradient of the line represents in context.

d

Find the y-intercept.

e

Describe what the y-intercept represents in context.

f

Find the restaurant's net profit if it has 310 customers for the week.

13

A diver starts at the surface of the water and begins to descend below the surface at a constant rate. The table below shows the depth of the diver over 4 minutes:

\text{Number of minutes passed, }x01234
\text{Depth of diver in metres, }y01.42.84.25.6
a

Calculate the increase in depth each minute.

b

Write a linear equation for the relationship between the number of minutes passed, x, and the depth, y, of the diver.

c

Calculate the depth of the diver after 6 minutes.

d

Calculate how long the diver takes to reach 12.6 metres beneath the surface.

14

In a study, scientists found that the more someone sleeps, the quicker their reaction time. The table below displays the findings:

\text{Number of hours of sleep } (x)012345
\text{Reaction time in seconds } (y)65.85.65.45.25
a

How much does the reaction time decrease for each extra hour of sleep?

b

Write an algebraic equation relating the number of hours of sleep (x) and the reaction time (y).

c

Calculate the reaction time for someone who has slept 4.5 hours.

d

Calculate the number of hours someone sleeps if they have a reaction time of 5.5 seconds.

15

A diver starts at the surface of the water and starts to descend below the surface at a constant rate. The table shows the depth of the diver over 5 minutes.

Number of minutes passed01234
Depth of diver in metres00.81.62.43.2
a

Graph the linear relationship represented in the table.

b

What is the increase in depth each minute?

c

State the gradient of the line.

d

Calculate the depth of the diver after 24 minutes.

16

Petrol costs a certain amount per litre. The table shows the cost of various amounts of petrol in dollars:

\text{Number of litres } (x\text{)}010203040
\text{Cost of petrol } (y\text{)}012.0024.0036.0048.00
a

Graph the linear relationship represented in the table.

b

How much does petrol cost per litre?

c

How much would 75 litres of petrol cost at this unit price?

17

Consider the following table that shows the temperature of a metal plate, in \degree\text{C}, after an amount of time, measured in minutes:

\text{Time }(x)12345
\text{Temperature }(y)1015202530
a

Graph the linear relationship represented in the table.

b

By how much is the temperature increasing each minute?

c

Find the initial temperature.

d

Hence form an equation relating x and y.

e

Find the temperature of the plate after 12 minutes.

18

The number of calories burned by the average person while dancing is modelled by the equation C = 8 m, where m is the number of minutes.

Sketch the graph of this equation to show the calories burnt after each 15-minute interval.

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m
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C
19

The number of university students studying computer science in a particular country is modelled by the equation S = 4 t + 12, where t is the number of years since 2000 and S is the number of students in thousands.

Sketch the graph of this equation to show the number of computer science students at the end of each 4-year period.

20

The amount of medication in a patient’s body \left(M \text{ mg}\right) gradually decreases over time \left(t \text{ hours}\right) according to the equation M = 12 - 2 t.

a

State how much medication, M, was present in the body inititally, at t = 0.

b

Find the value of t when M=0.

c

Hence, graph the line M = 12 - 2 t.

21

Beth’s income is based solely on the number of hours she works, and she is paid a fixed hourly wage. She earns \$750 for working 30 hours. Let y represent Beth’s income after working x hours.

a

Sketch a graph that displays her income against her hours worked.

b

Find the gradient of the line.

c

Explain the meaning of the gradient in this context.

d

Form an equation relating x and y.

e

Calculate Beth's income when she works 25 hours.

f

Calculate the number of hours that Beth must work to earn \$125.

22

The cost, y, for a business to operate, can be expressed in terms of x, the total number of hours it has operated for. The cost is \$120 an hour.

a

Sketch a graph that displays the cost against time.

b

State the gradient of the line.

c

Form an equation relating x and y.

d

Find the total cost for the business to operate for 28 hours.

e

Find the number of hours that the business needs to operate to incur a total cost of \$3840.

23

A ball is rolled down a slope. The table below shows the velocity (V) of the ball after a given number of seconds (t):

\text{Time in seconds } (t)012345
\text{Velocity in m/s } (V)1213.314.615.917.218.5
a

Plot the graph of the ball's velocity against time on a coordinate plane.

b

Calculate the gradient of the line.

c

What does the gradient represent in this context?

d

State the vertical intercept of the line.

e

What does the vertical intercept represent in this context?

f

Write an algebraic equation for the line, expressing V in terms of t.

g

Hence determine the velocity of the ball after 19 seconds. Round your answer to one decimal place.

24

The number of fish in a river is approximated over a five year period. The results are shown in the following table.

\text{Time in years }(t)012345
\text{Number of fish }(F)480046004400420040003800
a

Sketch a graph that corresponds to this information.

b

Calculate the gradient of the line.

c

What does the gradient represent in this context?

d

State the value of F when the line crosses the vertical axis.

e

Determine an equation for the line, using the given values.

f

Hence, determine the number of fish remaining in the river after 13 years.

g

Find the number of years, \left(t\right), until 2000 fish remain in the river.

Table of values
25

A racing car starts the race with 140 litres of fuel. From there, it uses fuel at a rate of 2 litres per minute. Complete the table of values:

\text{Number of minutes passed} \,(x)0510152070
\text{Amount of fuel left}\, (y)
26

There are 20 \text{ L} of water in a rainwater tank. It rains for a period of 24 hours and during this time the tank fills up at a rate of 8 \text{ L/h}. Complete the table of values:

\text{Number of hours passed }(x)046791112
\text{Amount of water in tank }(y)
27

The cost of a taxi ride C is given by C = 2.50 t + 3 where t is the duration of the trip in minutes. Complete the table of values:

\text{Time in minutes }(t)67891116
\text{Cost in dollars }(C)
28

The cost of a taxi ride is given by C = 5.5 t + 3, where t is the duration of the trip in minutes.

a

Calculate the cost of an 11-minute trip.

b

For every extra minute the trip takes, how much more will the trip cost?

c

What could the constant value of 3 represent in context?

29

A baseball is thrown vertically upward by a baseball player when he is standing on the ground, and the velocity of the baseball V (in metres per second) after T seconds is given by V = 120 - 32 T.

a

Complete the table of values:

\text{Time}01234
\text{Vertical Velocity}
b

State the gradient of the linear function.

c

Explain the negative value of V when T = 4.

30

The table shows the linear relationship between the number of plastic chairs manufactured, x, and the total manufacturing cost, y:

Number of plastic chairs51015
Cost (dollars)135185235
a

State the gradient of the linear function.

b

Form an equation relating x and y.

c

Find the y-intercept.

d

Find the total cost of manufacturing 25 plastic chairs.

e

Explain the meaning of the y-intercept in this context.

f

Explain the meaning of the gradient of the function in this context.

31

Petrol costs a certain amount per litre. The table shows the cost of various amounts of petrol in dollars:

\text{Number of litres }(x)010203040
\text{Cost of petrol }(y)016.4032.8049.2065.60
a

Find the cost of petrol per litre.

b

Write an equation linking the number of litres of petrol pumped \left(x\right) and the cost of the petrol \left(y\right).

c

Explain the meaning of the gradient in this context.

d

Calculate the cost of 47 \text{ L} petrol.

32

After Sally starts running, her heartbeat increases at a constant rate:

a

Complete the table:

\text{Number of minutes passed } (x\text{)}024681011
\text{Heart rate } (y\text{)}7581879399105
b

State the gradient of the line.

c

By how much is her heartbeat increasing each minute?

d

Explain the meaning of the y-intercept in this context.

33

After Mae starts running, her heart rate in beats per minute increases at a constant rate as shown in the following table:

\text{Number of minutes passed, }x024681012
\text{Heart rate, }y495561677379
a

Find the increase in heart rate for every 2 minutes.

b

Determine Mae's heart rate after 12 minutes.

c

Find the increase in heart rate per minute.

d

Write an equation that describes the relationship between the number of minutes passed, x, and Mae’s heart rate, y in the form y=mx+b.

34

Consider the points in the table, where the time (x) is measured in minutes:

\text{Time } (x\text{)}12345
\text{Temperature } (y\text{)}813182328
a

By how much is the temperature increasing each minute?

b

Find the initial temperature at time 0.

c

Find the algebraic rule between x and y.

d

Find the temperature after 17 minutes.

35

A racing car starts the race with 150 \text{ L} of fuel. From there, it uses fuel at a rate of 5\text{ L} per minute.

a

Complete the following table of values:

\text{Number of minutes passed } (x)05101520
\text{Amount of fuel left in the tank } (y)
b

Write an algebraic relationship linking the number of minutes passed \left(x\right) and the amount of fuel left in the tank \left(y\right).

c

How many minutes will it take for the car to run out of fuel?

36

A racing car starts the race with 250 litres of fuel. From there, it uses fuel at a rate of 5 litres per minute.

a

Complete the table of values:

\text{Number of minutes passed, }x0510152050
\text{Amount of fuel left in tank, }y
b

Determine an algebraic rule linking the number of minutes passed, x, and the amount of fuel left in the tank, y.

c

Explain the meaning of the gradient in this context.

37

Consider the pattern for blue boxes below:

a

Complete the table:

\text{Number of columns } (c)12351020
\text{Number of blue boxes } (b)
b

Write a formula that describes the relationship between the number of blue boxes (b) and the number of columns (c).

c

State the number of blue boxes, b, required for:

i

38 columns

ii

92 columns

d

State the number of columns, c, that would contain:

i

45 blue boxes

ii

51 blue boxes

38

A dam used to supply water to the neighbouring town had the following data recorded for its volume over a number of months:

\text{Month }(M)1234
\text{Volume in billions of litres } (V)11210611080
a

Is this relationship linear?

b

Explain a method to check whether the relationship is linear, without having to plot the points.

39

James recorded his savings (in dollars) over a few months in the graph given.

a

Complete the table:

\text{Months}1234
\text{Savings } \left(\$\right)
b

Is James correct if he estimates that he will have exactly \$60 in his savings by month 5?

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\text{Months}
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\text{Savings}
40

The graph shows the relationship between the number of cartons and the number of eggs in them.

Complete the table:

\text{Cartons}1234
\text{Eggs}
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5
\text{Cartons}
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9
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15
\text{Eggs}
41

The graph shows the relationship between water temperatures and surface air temperatures:

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-3
-2
-1
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5
\text{Water Temp}
-10
-8
-6
-4
-2
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10
\text{Air Temp}
a

Complete the table of values:

\text{Water Temperature } \left(\degree \text{C} \right)-3-2-10123
\text{Surface Air Temperature } \left(\degree \text{C} \right)
b

Write an algebraic equation representing the relationship between the water temperature (x) and the surface air temperature (y).

c

Find the surface air temperature when the water temperature is 14 \degree \text{C}.

d

Find the water temperature when the surface air temperature is 23 \degree \text{C}.

42

Let the height of a candle be y \text{ cm} . If the candle is lit, the height decreases according to the equation y = - 2 t + 8, where t is the elapsed time in minutes.

a

Complete the table of values:

\text{Time }(t \text{ min})0123
\text{Height of candle }(y \text{ cm})
b

Sketch the graph of y = - 2 t + 8.

c

Calculate the time when y=0.

d

The height of candle and the time elapsed must be non-negative. Hence, state the only posible values of t.

43

Let the volume of water in a tank be V \text{ L} . If the tank is initially empty, then the amount of water in the tank is given by V = 5 t where t is the elapsed time in minutes and 5 is the rate that the tank fills in \text{L/min}.

a

Complete the table of values below:

\text{Time }(t \text{ min})0123
\text{Volume of water }(V \text{ cm})
b

Sketch the graph of V = 5 t.

c

The volume of the tank is 15 \text{ L} and the time elapsed is non-negative. Hence, state the only posible values of t.

44

A car travels at an average speed of 75\text{ km/h}.

a

Complete the table of values for D = 75 t, where D is the distance travelled in kilometres and t is the time taken in hours:

t012345
D
b

How far will the car travel in 9 hours?

c

Sketch the graph of D = 75 t on a coordinate plane.

d

State the gradient of the line.

e

How long would it take for the car to travel a distance of D=675\text{ km} at the given speed?

45

It starts raining and an empty rainwater tank fills up at a constant rate of 2 litres per hour. By midnight, there are 20 litres of water in the rainwater tank. As it rains, the tank continues to fill up at this rate.

a

Complete the table of values:

\text{Number of hours passed since midnight } (x)012344.510
\text{Amount of water in tank } (y)20 22 24
b

Sketch the graph depicting the situation on a coordinate plane.

c

Write an algebraic relationship linking the number of hours passed since midnight (x) and the amount of water in the tank (y) in the form y=mx+b.

d

Calculate the value of x when the tank is empty, when y=0.

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Outcomes

1.3.3.1

use graphs in practical situations

1.3.3.2

interpret graphs in practical situations [complex]

1.3.3.3

draw graphs from given data to represent practical situations [complex]

1.3.3.4

interpret the point of intersection and other important features (𝑥 and 𝑦 intercepts) of given graphs of two linear functions drawn from practical contexts [complex]

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