| Date | May 2011 | Marks available | 3 | Reference code | 11M.1.sl.TZ1.9 |
| Level | SL only | Paper | 1 | Time zone | TZ1 |
| Command term | Calculate | Question number | 9 | Adapted from | N/A |
Question
The probability that it rains today is \(0.4\) . If it rains today, the probability that it will rain tomorrow is \(0.8\) . If it does not rain today, the probability that it will rain tomorrow is \(0.7\) .
Complete the tree diagram below.
[3]
a.
Calculate the probability of rain tomorrow.
[3]
b.
Markscheme
(A1)(A1)(A1) (C3)
Note: Award (A1) for each correct pair.
[3 marks]
a.
\(0.4 \times 0.8 + 0.6 \times 0.7\) (A1)(ft)(M1)
Notes: Award (A1)(ft) for two consistent products from tree diagram, (M1) for addition of their products. Follow through from their tree diagram provided all probabilities are between 0 and 1.
\( = 0.74\) (A1)(ft) (C3)
[3 marks]
b.
Examiners report
Part a of this question was well answered, however part b caused many problems. Candidates did not seem to know how to find the probability of the combined events.
a.
Part a of this question was well answered, however part b caused many problems. Candidates did not seem to know how to find the probability of the combined events.
b.
Syllabus sections
Topic 3 - Logic, sets and probability » 3.7 » Probability of combined events, mutually exclusive events, independent events.
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