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Date May 2021 Marks available 2 Reference code 21M.1.SL.TZ1.7
Level Standard Level Paper Paper 1 Time zone Time zone 1
Command term Find Question number 7 Adapted from N/A

Question

Professor Wei observed that students have difficulty remembering the information presented in his lectures.

He modelled the percentage of information retained, R, by the function R(t)=100e-pt, t0, where t is the number of days after the lecture.

He found that 1 day after a lecture, students had forgotten 50% of the information presented.

Based on his model, Professor Wei believes that his students will always retain some information from his lecture.

Find the value of p.

[2]
a.

Use this model to find the percentage of information retained by his students 36 hours after Professor Wei’s lecture.

[2]
b.

State a mathematical reason why Professor Wei might believe this.

[1]
c.

Write down one possible limitation of the domain of the model.

[1]
d.

Markscheme

EITHER

50=100e-1×p  OR  0.5=e-1×p              (M1)


OR

 

THEN

0.693  (0.693147, ln2)              A1


[2 marks]

a.

R1.5=100e-0.693147×1.5               (M1)

35.4%  35.3553             A1


[2 marks]

b.

Rt>0  OR  Rt has a horizontal asymptote             R1


[1 mark]

c.

Award A1 for one reasonable limitation of the domain:         A1

small values of t produce unrealistic results

R0=100%

large values of t are not possible

people do not live forever

model is not valid at small or large values of t


The reason should focus on the domain t0. Do not accept answers such as:

recollection varies for different people

memories are discrete not continuous

the nature of the information will change how easily it is recalled

emotional/physical stress can affect recollection/concentration


Note: Do not accept t0 as this is a limitation that has been given in the question.


[1 mark]

d.

Examiners report

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

Syllabus sections

Topic 2—Functions » SL 2.5—Modelling functions
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Topic 2—Functions

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