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Date November 2020 Marks available 1 Reference code 20N.1.SL.TZ0.T_14
Level Standard Level Paper Paper 1 (with calculator from previous syllabus) Time zone Time zone 0
Command term Question number T_14 Adapted from N/A

Question

Andre will play in the semi-final of a tennis tournament.

If Andre wins the semi-final he will progress to the final. If Andre loses the semi-final, he will not progress to the final.

If Andre wins the final, he will be the champion.

The probability that Andre will win the semi-final is p. If Andre wins the semi-final, then the probability he will be the champion is 0.6.

The probability that Andre will not be the champion is 0.58.

Complete the values in the tree diagram.

[1]
a.

Find the value of p.

[2]
b.

Given that Andre did not become the champion, find the probability that he lost in the semi-final.

[3]
c.

Markscheme

* This question is from an exam for a previous syllabus, and may contain minor differences in marking or structure. It appeared in a paper that permitted the use of a calculator, and so might not be suitable for all forms of practice.

       (A1)   (C1)


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

 

[1 mark]

a.

p×0.4+1-p=0.58       (M1)


Note:
Award (M1) for multiplying and adding correct probabilities for losing equated to 0.58.

OR

p×0.6=1-0.58       (M1)


Note:
 Award (M1) for multiplying correct probabilities for winning equated to 1-0.58  or  0.42.

p= 0.7       (A1)(ft)      (C2)


Note: Follow through from their part (a). Award the final (A1)(ft) only if their p is within the range 0<p<1.


[2 marks]

b.

0.30.58 1-0.70.58       (A1)(ft)(A1)


Note:
Award (A1)(ft) for their correct numerator. Follow through from part (b). Award (A1) for the correct denominator.

OR

0.30.3+0.7×0.4       (A1)(ft)(A1)(ft)


Note:
 Award (A1)(ft) for their correct numerator. Follow through from part (b). Award (A1)(ft) for their correct calculation of Andre losing the semi-final or winning the semi-final and then losing in the final. Follow through from their parts (a) and (b).

1529 0.517, 0.517241, 51.7%       (A1)(ft)      (C3)


Note: Follow through from parts (a) and (b).


[3 marks]

c.

Examiners report

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

Syllabus sections

Topic 4—Statistics and probability » SL 4.6—Combined, mutually exclusive, conditional, independence, prob diagrams
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Topic 4—Statistics and probability

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