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Date November 2020 Marks available 2 Reference code 20N.1.SL.TZ0.T_6
Level Standard Level Paper Paper 1 Time zone Time zone 0
Command term Find Question number T_6 Adapted from N/A

Question

Srinivasa places the nine labelled balls shown below into a box.

Srinivasa then chooses two balls at random, one at a time, from the box. The first ball is not replaced before he chooses the second.

Find the probability that the first ball chosen is labelled A.

[1]
a.i.

Find the probability that the first ball chosen is labelled A or labelled N.

[1]
a.ii.

Find the probability that the second ball chosen is labelled A, given that the first ball chosen was labelled N.

[2]
b.

Find the probability that both balls chosen are labelled N.

[2]
c.

Markscheme

39 13, 0.333, 0.333333, 33.3%        (A1)   (C1)


[1 mark]

a.i.

59 0.556, 0.555555, 55.6%        (A1)   (C1)


[1 mark]

a.ii.

38 0.375, 37.5%        (A1)(A1)   (C2)


Note:
Award (A1) for correct numerator, (A1) for correct denominator.


[2 marks]

b.

29×18        (M1)


Note:
Award (M1) for a correct compound probability calculation seen.


272 136, 0.0278, 0.0277777, 2.78%       (A1)  (C2)


[2 marks]

c.

Examiners report

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

Syllabus sections

Topic 4—Statistics and probability » SL 4.5—Probability concepts, expected numbers
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Topic 4—Statistics and probability » SL 4.6—Combined, mutually exclusive, conditional, independence, prob diagrams
Topic 4—Statistics and probability

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