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Date November 2016 Marks available 4 Reference code 16N.1.sl.TZ0.12
Level SL only Paper 1 Time zone TZ0
Command term Find Question number 12 Adapted from N/A

Question

On a work day, the probability that Mr Van Winkel wakes up early is \(\frac{4}{5}\).

If he wakes up early, the probability that he is on time for work is \(p\).

If he wakes up late, the probability that he is on time for work is \(\frac{1}{4}\).

The probability that Mr Van Winkel arrives on time for work is \(\frac{3}{5}\).

Complete the tree diagram below.

N16/5/MATSD/SP1/ENG/TZ0/12.a

[2]
a.

Find the value of \(p\).

[4]
b.

Markscheme

N16/5/MATSD/SP1/ENG/TZ0/12.a/M     (A1)(A1)     (C2)

 

Note:     Award (A1) for each correct pair of probabilities.

 

[2 marks]

a.

\(\frac{4}{5}p + \frac{1}{5} \times \frac{1}{4} = \frac{3}{5}\)     (A1)(ft)(M1)(M1)

 

Note:     Award (A1)(ft) for two correct products from part (a), (M1) for adding their products, (M1) for equating the sum of any two probabilities to \(\frac{3}{5}\).

 

\((p = ){\text{ }}\frac{{11}}{{16}}{\text{ }}(0.688,{\text{ }}0.6875)\)    (A1)(ft)     (C4)

 

Note:     Award the final (A1)(ft) only if \(0 \leqslant p \leqslant 1\). Follow through from part (a).

 

[4 marks]

b.

Examiners report

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

Syllabus sections

Topic 3 - Logic, sets and probability » 3.7 » Probability of combined events, mutually exclusive events, independent events.
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