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A-LevelMathematicsProbability and statistics9709/61 · May/June 2021 · Q14 Marks

Accidents at two factories occur randomly and independently. On average, the numbers of accidents per month are 3.1 at factory A and 1.7 at factory B.

  1. Find the probability that the total number of accidents in the two factories during a 2-month period is more than 3.[4]

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

  1. [M1] Attempt combined mean. Allow 3.1 + 1.7 for M1
  2. [A1] Correct mean
  3. [M1] Allow incorrect mean. Allow one end error.
  4. [A1] SC If 9.6 seen and unsupported 0.986 M1A1B1. SC Unsupported correct answer of 0.986 only if 9.6 also not seen scores B2 only.

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About this question

Topic
Probability and statistics, A-Level Mathematics (syllabus 9709). Structured question, 4 marks.
Source
A-Level Mathematics, May/June 2021 Paper 6 Variant 1, question 1.

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