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Edexcel IGCSE Math B 10.G product rule

Practise product-rule questions by multiplying probabilities along the required stages and comparing the result with any decision condition.

Syllabus
First assessment 2018
Course
Math B 4MB1

Exam points

  • Multiply probabilities for repeated events such as rolling 2 then 5 in order.
  • Use product-rule calculations for two-stage game or test scenarios carefully.
  • Compare the final probability with a threshold when the question asks for a decision.

10.G Product rule question 1

[Maximum number: 2]

To pass a course, Preety has to pass two tests, test A and test B.
Each test only has to be passed once.
Passing test A and passing test B are independent events.
Preety has three attempts to pass test A.
The probability that she passes test A on her first attempt is 35\frac{3}{5}
If she fails on her first attempt, the probability that she passes on her second attempt is 25\frac{2}{5}
If she fails on her second attempt, the probability that she passes on her third attempt is 38\frac{3}{8}

Preety decides to take the two tests only if the probability that she passes the course is greater than 0.5.

State whether or not Preety should take the two tests.
Give a reason for your answer.

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