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2.3 Probability

2.3 Probability

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Question 120

An IT security firm analyzes 250 detected cyber-threats over a weekend. Threats are classified into three categories: Malware (MMM), Phishing (PPP), and Denial of Service (DDD).

  • 140 involve Malware,
  • 120 involve Phishing,
  • 105 involve Denial of Service,
  • 65 involve both Malware and Phishing,
  • 55 involve both Phishing and Denial of Service,
  • 45 involve both Malware and Denial of Service,
  • 20 involve all three categories.
a.

Draw a Venn diagram to represent this information.

[3]
b.

A threat is selected at random from the database. Find the probability that this threat involves:

none of the three categories,

[1]
c.

A threat is selected at random from the database. Find the probability that this threat involves:

Denial of Service only.

[1]
d.

Threats categorized as 'Advanced Persistent Threats' (APT) are those that involve both Phishing and Denial of Service. Given that a randomly selected threat is an APT,

find the probability that this threat also involves Malware.

[2]
Markscheme

2.3 Probability Questions

  1. A Level
  2. /Maths
  3. /2.3 Probability

200 exam-style questions on OCR (MEI) A Level Maths 2.3 Probability, covering 2.3.1 Calculate the probability of an event, 2.3.2 Complementary events, 2.3.3 Expected frequency of an event, 2.3.4 Diagrams to calculate probabilities, 2.3.5 Mutually exclusive and independent events, 2.3.6 Add probabilities for mutually exclusive events, 2.3.7 Multiply probabilities for independent events, 2.3.8 Mutually exclusive and independent events (notation) (A-level only), 2.3.9 Venn diagrams for probabilities (A-level only), 2.3.10 Conditional probabilities (A-level only), and 2.3.11 Independence via conditional probability (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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