Madison Tyler Holdings Interview Question: There are 5 coins on a table.... | Glassdoor

Interview Question

Trading Analyst Interview Sydney (Australia)

There are 5 coins on a table. One of them has a heads on

  both sides. If you pick up one of the coins and flip it 5 times and get heads each time what is the probability that you have picked up the double sided coin?

Interview Answer

3 Answers



Interview Candidate on May 24, 2011

Total possibilities that lead to 5 heads in 5 flips:

chose the double head coin + 2^5 possible results = 32
chose any of 4 other coins and flipped HHHHH = 4

So the total number of states that lead to 5 heads is 36. In 32 of them, you chose the double-headed coin, so your chances of having picked the double headed coin, given that you flipped 5 heads is

32/36 = 8/9

fizixgeek on Feb 14, 2012

There is only one double sided coin. So the probability is equal to the probability of getting the double sided coin and flipping five heads which is (1/5)*1 plus the probability of getting one of the other four normal coins and flipping 5 heads which is (4/5)*(1/2)^5

Anonymous on Jun 13, 2014

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