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Date May 2022 Marks available 2 Reference code 22M.1.SL.TZ1.12
Level Standard Level Paper Paper 1 Time zone Time zone 1
Command term Determine Question number 12 Adapted from N/A

Question

A company’s profit per year was found to be changing at a rate of

dPdt=3t2-8t

where P is the company’s profit in thousands of dollars and t is the time since the company was founded, measured in years.

Determine whether the profit is increasing or decreasing when t=2.

[2]
a.

One year after the company was founded, the profit was 4 thousand dollars.

Find an expression for P(t), when t0.

[4]
b.

Markscheme

METHOD 1

(when t=2)

dPdt=-4   OR   dPdt<0 (equivalent in words)   OR   322-82=-4          M1

therefore P is decreasing             A1

 

METHOD 2

sketch with t=2 indicated in 4th quadrant   OR   t-intercepts identified          M1

therefore P is decreasing             A1

 

[2 marks]

a.

Pt=  t3-4t2+c            A1A1

4=13-412+c            (M1)


Note: Award M1 for substituting (1, 4) into their equation with +c seen.


c=7

Pt=t3-4t2+7            A1

 

[4 marks]

b.

Examiners report

Even some weaker candidates were able to score in this part of the question as many candidates understood the process required to determine whether the profit is increasing or decreasing.

a.

Many candidates failed to recognize that they needed to integrate the original function. Of the few that attempted to find the value of the constant the vast majority substituted 4000 rather than 4. So, a correct final expression for P(t) was rarely seen.

b.

Syllabus sections

Topic 5—Calculus » SL 5.2—Increasing and decreasing functions
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