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Functions, 2ADV EQ-Bank 5 MC

The time taken to clean a warehouse varies inversely with the number of cleaners employed.

It takes 8 cleaners 60 hours to clean a warehouse.

Working at the same rate, how many hours would it take 10 cleaners to clean the same warehouse.

  1. 45
  2. 48
  3. 62
  4. 75
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`B`

Show Worked Solution

`text{Time to clean}\ (T) prop 1/text{Number of cleaners (C)}`

`T=k/C`

`text(When)\ \ T=60, C=8:`

`60` `=k/8`
`k` `=480`

 
`text{Find}\ \ T\ \ text(when)\ \ C=10:`

`T=480/10=48\ text(hours)`

`=>  B`

Filed Under: Direct and Inverse Variation Tagged With: Band 4, smc-6383-30-\(\propto \dfrac{k}{x^{n}} \), smc-6383-50-Real World Examples

Functions, 2ADV EQ-Bank 10

The number of trees that can be planted along the fence line of a paddock varies inversely with the distance between each tree.

There will be 108 trees if the distance between them is 5 metres.

  1. How many trees can be planted if the distance between them is 6 metres?   (2 marks)

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  2. What is the distance between the trees if 120 trees are planted.   (1 mark)

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a.   `90`

b.   `4.5\ text(metres)`

Show Worked Solution

a.   `t \prop 1/d \ \ =>\ \ t=k/d`

`108` `= k/5`
`k` `= 540`

 
`text(Find)\ t\ \text(when)\ \ d = 6:`

`t= 540/6= 90`
 

b.   `text(Find)\ d\ text(when)\ \ t = 120:`

`120` `= 540/d`
`d` `= 540/120= 4.5\ text(metres)`

Filed Under: Direct and Inverse Variation Tagged With: Band 4, smc-6383-30-\(\propto \dfrac{k}{x^{n}} \), smc-6383-50-Real World Examples

Functions, 2ADV EQ-Bank 8

The intensity of light \((I)\), measured in lux, from a lamp varies inversely with the square of the distance from the lamp \((d)\), measured in metres.

At a distance of 2.2 metres from the lamp, the light intensity is 400 lux.

What is the light intensity at a distance of 5.0 metres from the lamp?   (2 marks)

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\(77.44\ \text{lux}\)

Show Worked Solution

\(I \propto \dfrac{k}{d^2} \ \Rightarrow \ I=\dfrac{k}{d^2}\)

\(\text{Find k given} \ \ I=400 \ \ \text {when} \ \ d=2.2:\)

\(400=\dfrac{k}{2.2^2} \ \Rightarrow \ k=1936\)
 

\(\text{Find \(I\) when \(\ d=5\):}\)

\(I=\dfrac{1936}{5.0^2}=77.44\ \text{lux}\)

Filed Under: Direct and Inverse Variation Tagged With: Band 4, smc-6383-30-\(\propto \dfrac{k}{x^{n}} \), smc-6383-50-Real World Examples

Functions, 2ADV EQ-Bank 9

The quantity \(y\) varies inversely with the square of \(x\).

When  \(x = 4, \ y = 10\).

Find the value of \(y\) when \(x = 8\).   (2 marks)

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\(y=\dfrac{5}{2}\)

Show Worked Solution

\(y \propto \dfrac{1}{x^2}\ \ \Rightarrow\ \ y= \dfrac{k}{x^2}\)

\(\text{When}\ \ x=4, \ y=10:\)

\(10= \dfrac{k}{4^2}\ \ \Rightarrow\ \ k=160\)
 

\(\text{Find}\ y\ \text{when}\ x=8:\)

\(y=\dfrac{160}{8^2}=\dfrac{5}{2}\)

Filed Under: Direct and Inverse Variation, Further Functions and Relations (Y11) Tagged With: Band 4, smc-6383-30-\(\propto \dfrac{k}{x^{n}} \), smc-987-60-Proportional

Functions, 2ADV F1 2022 HSC 12

A student believes that the time it takes for an ice cube to melt (`M` minutes) varies inversely with the room temperature `(T^@ text{C})`. The student observes that at a room temperature of `15^@text{C}` it takes 12 minutes for an ice cube to melt.

  1. Find the equation relating `M` and `T`.    (2 marks)

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  2. By first completing this table of values, graph the relationship between temperature and time from `T=5^@C` to `T=30^@ text{C}`.   (2 marks)
     

\begin{array} {|c|c|c|c|}
\hline  \ \ T\ \  & \ \ 5\ \  & \ 15\  & \ 30\  \\
\hline M &  &  &  \\
\hline \end{array}

 
                   

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a.    `M=180/T`

 b.    

\begin{array} {|c|c|c|c|}
\hline  \ \ T\ \  & \ \ 5\ \  & \ 15\  & \ 30\  \\
\hline M & 36 & 12 & 6 \\
\hline \end{array}       

 

Show Worked Solution
a.    `M` `prop 1/T`
  `M` `=k/T`
  `12` `=k/15`
  `k` `=15 xx 12`
    `=180`

 
`:.M=180/T`
 


♦ Mean mark (a) 49%.

b.   

\begin{array} {|c|c|c|c|}
\hline  \ \ T\ \  & \ \ 5\ \  & \ 15\  & \ 30\  \\
\hline M & 36 & 12 & 6 \\
\hline \end{array}

Filed Under: Direct and Inverse Variation, Further Functions and Relations (Y11), Variation and Rates of Change Tagged With: 2adv-std2-common, Band 4, Band 5, common-content, num-title-ct-patha, num-title-qs-hsc, smc-4239-30-a prop 1/b, smc-6383-30-\(\propto \dfrac{k}{x^{n}} \), smc-987-30-Reflections and Other Graphs, smc-987-60-Proportional

Functions, 2ADV F1 EQ-Bank 7

The current of an electrical circuit, measured in amps `(A)`, varies inversely with its resistance, measured in ohms `(R)`.

When the resistance of a circuit is 28 ohms, the current is 3 amps.

What is the current when the resistance is 8 ohms?   (2 marks)

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`10.5`

Show Worked Solution

`A \prop 1/R\ \ =>\ \ A=k/R`

`text(When)\ \ A=3, \ R=28:`

`3` `=k/28`  
`k` `=84`  

 
`text(Find)\ A\ \text{when}\ R=8:`

`A=84/8=10.5`

Filed Under: Direct and Inverse Variation, Further Functions and Relations (Y11) Tagged With: Band 4, smc-6383-30-\(\propto \dfrac{k}{x^{n}} \), smc-987-60-Proportional

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