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Multiplication rule of probability


In a lottery there are a 100 tickets. Out of these 10 contain the prize of a playstation where as 90 are empty.
Satyam buys a ticket and checks if he has won the prize. If he has not, he buys another ticket. He goes on like this until he wins the prize.
Find the probability that Satyam buys a total of 3 tickets.
  • Your answer should be
  • a simplified proper fraction, like 3, slash, 5
  • a simplified improper fraction, like 7, slash, 4