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HigherNon-calculatorP8 Independent and dependent combined events

Question 1 · 3 marks

Spec and skills
  • Paper scope: Paper 1: non-calculator practice
  • Spec P8
  • Spec P9
  • Original practice question
  • Answer and supported method checks
A box contains n batteries, exactly 4 of which are faulty. Two batteries are selected at random without replacement. The probability that both are faulty is 1/13. Work out n. You must show your working.