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2.3 Probability

2.3 Probability

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Question 101

A cybersecurity firm analyzed 120 security incidents recorded in a single month. Each incident was categorized by its severity level: Low (LLL), Medium (MMM), or High (HHH). The firm tracked four specific types of threats: Phishing, Malware, DDoS, and Data Breach. The total counts for each severity category were 30 incidents of Low severity, 50 of Medium severity, and 40 of High severity. The occurrences are detailed in the table below:

Threat CategoryLow severity (L)Medium severity (M)High severity (H)Phishing81222Malware101518DDoS253510Data Breach587 \begin{array}{|l|c|c|c|} \hline \text{Threat Category} & \text{Low severity } (L) & \text{Medium severity } (M) & \text{High severity } (H) \\ \hline \text{Phishing} & 8 & 12 & 22 \\ \hline \text{Malware} & 10 & 15 & 18 \\ \hline \text{DDoS} & 25 & 35 & 10 \\ \hline \text{Data Breach} & 5 & 8 & 7 \\ \hline \end{array} Threat CategoryPhishingMalwareDDoSData Breach​Low severity (L)810255​Medium severity (M)1215358​High severity (H)2218107​​
a.

Determine the probability that a randomly selected security incident from this study: (i) is a Malware threat and has High severity; (ii) is a DDoS threat; (iii) is a Phishing threat, given that it has Medium severity.

[5]
b.

For the incidents classified as Low severity, explain why the events 'is a Malware threat' and 'is a DDoS threat' are not mutually exclusive.

[3]
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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