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Date November 2021 Marks available 3 Reference code 21N.1.SL.TZ0.4
Level Standard Level Paper Paper 1 (without calculator) Time zone Time zone 0
Command term Find Question number 4 Adapted from N/A

Question

Box 1 contains 5 red balls and 2 white balls.

Box 2 contains 4 red balls and 3 white balls.

A box is chosen at random and a ball is drawn. Find the probability that the ball is red.

[3]
a.

Let A be the event that “box 1 is chosen” and let R be the event that “a red ball is drawn”.

Determine whether events A and R are independent.

[2]
b.

Markscheme

valid approach to find PR                 (M1)

tree diagram (must include probabilty of picking box) with correct required probabilities

OR   PRB1+PRB2   OR   PRB1PB1+PRB2PB2

57·12+47·12                 (A1)

PR=914                A1

 

[3 marks]

a.

events A and R are not independent, since 914·12514  OR  57914  OR  5912

OR an explanation e.g. different number of red balls in each box                A2

 

Note: Both conclusion and reasoning are required. Do not split the A2.

 

[2 marks]

b.

Examiners report

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

Syllabus sections

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