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Algebra, STD2 A4 2021 HSC 35 (Adapted)

A toy store releases a limited edition LEGO set for $20 each. At this price, 3000 LEGO sets are sold each week and the revenue is  `3000 xx 20=$60\ 000`.

The toy store considers increasing the price. For every dollar price increase, 15 fewer LEGO sets will be sold.

If the toy store charges `(20+x)` dollars for each LEGO set, a quadratic model for the revenue raised, `R`, from selling them is

`R=-15x^2+2700x+60\ 000`

 


 

  1. What price should be charged per LEGO set to maximise the revenue?   (2 marks)

  2. How many LEGO sets are sold when the revenue is maximised?   (2 marks)

  3. Find the value of the intercept of the parabola with the vertical axis.   (1 mark) 

Show Answers Only

a.   `$110`

b.    `1650`

c.   `$60\ 000`

Show Worked Solution

a.   `text{Highest revenue}\ (R_text{max})\ text(occurs halfway between)\ \ x= -20 and x=200.`

`text{Midpoint}\ =(-20 + 200)/2 = 90`

`:.\ text(Price of LEGO set for)\ R_text(max)`

`=90 + 20`

`=$110`
 

b.  `text{LEGO sets sold when}\ R_{max}`

`=3000-(90 xx 15)`

`=1650`
 

c.   `ytext(-intercept → find)\ R\ text(when)\ \ x=0:`

`R` `= -15(0)^2 + 2700(0) + 60\ 000`
  `=$60\ 000`

Algebra, STD2 A4 2017 HSC 28e (Adapted)

Sage brings 60 cartons of unpasteurised milk to the market each week. Each carton currently sells for $4 and at this price, all 60 cartons are sold each weekend.

Sage considers increasing the price to see if the total income can be increased.

It is assumed that for each $1 increase in price, 6 fewer cartons will be sold.

A graph showing the relationship between the increase in price per carton and the income is shown below.

 


 

  1. What price per carton should be charged to maximise the income?   (1 mark)

  2. What is the number of cartons sold when the income is maximised?   (1 mark)

  3. The cost of running the market stall is $40 plus $1.50 per carton sold.

    Calculate Sage's profit when the income earned from a day selling at the market is maximised.   (2 marks)

Show Answers Only

a.   `$7`

b.   `42`

c.   `$191`

Show Worked Solution

a.   `text(Graph is highest when increase = $3)`

`:.\ text(Carton price)\ = 4 + 3= $7`
 

b.   `text(Cartons sold)\ =60-(3 xx 6)=42`
  

c.   `text{Cost}\ = 42 xx 1.50 + 40 = $103`

`:.\ text(Profit when income is maximised)`

`= (42 xx 7)-103`

`= $191`

Algebra, STD2 A4 2013 HSC 22 MC (Adapted)

Jevin wants to build a rectangular chicken pen. He has 32 metres of fencing and will use a barn wall as one side of the pen. The width of the pen is \(d\) metres.
 

Which equation gives the area, \(P\), of the chicken pen?

  1. \(P = 16d-d^2\)
  2. \(P = 32d-d^2\)
  3. \(P = 16d-\dfrac{d^2}{2}\)
  4. \(P = 16d-2d^2\) 
Show Answers Only

\(C\)

Show Worked Solution
♦♦♦ Mean mark 24% (lowest mean of any MC question in 2013 exam)

\(\text{Length of pen}\ = \dfrac{1}{2}(32-d)\)

\(\text{Area}\ =d \times \dfrac{1}{2}(32-d)=16d-\dfrac{d^2}{2}\)

 \(\Rightarrow C\)

Algebra, STD2 A4 2022 HSC 9 MC (Adapted)

An object is projected vertically into the air. Its height, \(h\) metres, above the ground after \(t\) seconds is given by  \(h=-5 t^2+80 t\).
 

How far does the object travel in the first 10 seconds?

  1. 300 metres
  2. 320 metres
  3. 340 metres
  4. 480 metres
Show Answers Only

\(C\)

Show Worked Solution

\(\text{By symmetry (or graph), object reaches max height at}\ \ t=8\ \text{seconds.}\)

\(\text{Find}\ h\ \text{when}\ \ t=8:\)

\(h=-5 \times 8^2-10 \times 8= 320 \)

\(\text{When}\ \ t=10\ \ \Rightarrow\ \ h=300\ \text{(from graph)}\)

\(\therefore\ \text{Total distance}\ = 320 + 20=340\ \text{metres}\)

\(\Rightarrow C\)