23. The probability that Kathy cycles to work on Monday is 0·6. If she cycles to work on Monday, the probability that she cycles to work on Tuesday is 0·3. If she does not cycle to work on Monday, the probability that she does not cycle to work on Tuesday is 0·1.
(a) Complete the tree diagram. [1]
(b) Calculate the probability that Kathy cycles to work on both Monday and Tuesday. [2]
(c) Calculate the probability that Kathy does not cycle to work on either day. [2]
Mark scheme (a)
Scheme
Marks
Comments
0.7 AND 0.9 correctly placed
B1
Mark scheme (b)
Scheme
Marks
Comments
0.6 × 0.3 oe
M1
0.18 oe
A1
ignore attempts to convert to a different form; ignore embellishments such as unlikely, even if incorrect
Mark scheme (c)
Scheme
Marks
Comments
0.4 × 0.1 oe
M1
0.04 oe
A1
ignore attempts to convert to a different form; ignore embellishments such as unlikely, even if incorrect
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