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2.3 Probability

2.3 Probability

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Question 163

A jar contains a large number of marbles. There are two colors of marbles in the jar:

  • 30% are Red (R)
  • 70% are Blue (B)

A student picks a marble at random, records its color, and replaces it in the jar. They then pick a second marble at random.

a.

Calculate the probability that both marbles picked are the same color.

[2]
b.

Find the probability that both marbles are Red, given that at least one of the marbles is Red.

[4]
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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