Sequential selection until condition met

A question is this type if and only if it involves selecting items one at a time without replacement until a specific condition is satisfied (e.g., obtaining both blue socks).

1 questions · Standard +0.3

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Edexcel S1 2018 January Q6
11 marks Standard +0.3
  1. Anju has a bag that contains 5 socks of which 2 are blue.
Anju randomly selects socks from the bag, one sock at a time. She does not replace any socks but continues to select socks at random until she has both blue socks. The discrete random variable \(S\) represents the total number of socks that Anju has selected.
  1. Write down the value of \(\mathrm { P } ( S = 1 )\)
  2. Find \(\mathrm { P } ( S > 2 )\)
  3. Find \(\mathrm { P } ( S = 3 )\)
  4. Given that the second sock selected is blue, find the probability that Anju selects exactly 3 socks.
  5. Find \(\mathrm { P } ( S = 5 )\)