| Date | November 2009 | Marks available | 1 | Reference code | 09N.1.sl.TZ0.9 |
| Level | SL only | Paper | 1 | Time zone | TZ0 |
| Command term | Find | Question number | 9 | Adapted from | N/A |
Question
The probability that it will snow tomorrow is 0.3.
If it snows tomorrow the probability that Chuck will be late for school is 0.8.
If it does not snow tomorrow the probability that Chuck will be late for school is 0.1.
Complete the tree diagram below.
[3]
a.
Find the probability that it does not snow tomorrow and Chuck is late for school.
[1]
b.
Find the probability that Chuck is late for school.
[2]
c.
Markscheme
(A1)(A1)(A1) (C3)
Note: Award (A1) for each correct pair.
[3 marks]
a.
\(0.7 \times 0.1\)
\( = 0.07(\frac{7}{{100}},{\text{ }}7\% )\) (A1)(ft) (C1)
[1 mark]
b.
\(0.3 \times 0.8 + 0.07\) (M1)
\( = 0.31(\frac{{31}}{{100}},{\text{ }}31\% )\) (A1)(ft)
Note: In (b) and (c) follow through from sensible answers only i.e. not a probability greater than one. (C2)
[2 marks]
c.
Examiners report
This question was answered well.
a.
This question was answered well.
b.
A few students were unable to do part (c).
c.
Syllabus sections
Topic 3 - Logic, sets and probability » 3.7 » Probability of combined events, mutually exclusive events, independent events.
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