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Date May 2021 Marks available 2 Reference code 21M.1.SL.TZ1.4
Level Standard Level Paper Paper 1 Time zone Time zone 1
Command term Find Question number 4 Adapted from N/A

Question

The price of gas at Leon’s gas station is $1.50 per litre. If a customer buys a minimum of 10 litres, a discount of $5 is applied.

This can be modelled by the following function, L, which gives the total cost when buying a minimum of 10 litres at Leon’s gas station.

L(x)=1.50x-5, x10

where x is the number of litres of gas that a customer buys.

Find the total cost of buying 40 litres of gas at Leon’s gas station.

[2]
a.

Find L-1(70).

[2]
b.

The price of gas at Erica’s gas station is $1.30 per litre. A customer must buy a minimum of 10 litres of gas. The total cost at Erica’s gas station is cheaper than Leon’s gas station when x>k.

Find the minimum value of k.

[3]
c.

Markscheme

L40=1.50×40-5                      (M1)

=$55              A1


[2 marks]

a.

70=1.50x-5                     (M1)

x= 50 litres             A1


[2 marks]

b.

1.30x                     (A1)

1.30x<1.50x-5                     (M1)


Note: Award M1 for a graph showing two intersecting linear functions, provided one function has a y-intercept of 0 and the other function has a negative y-intercept.


(minimum value of k=) 25                     A1


Note: Accept x>25.


[3 marks]

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Topic 2—Functions » SL 2.2—Functions, notation domain, range and inverse as reflection
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