Interview Question

Trader Interview

You flip 4 fair coins and get x dollars where x is the

  number of heads squared. What are your expected winnings?
Answer

Interview Answer

7 Answers

5

5

Interview Candidate on Jan 24, 2012
1

(1^2 + 2^2 + 3^2 + 4^2)/4 = (1 + 4 + 9 + 16)/4 = 30/4 = 7.5

Anonymous on Feb 1, 2012
2

7.5 is obviously wrong...the probability distribution isn't uniform.

Sam on Feb 1, 2012
0

1/16*(1*4+2^2*6+3^2*4+4^2*1) = 110/16 = 55/8

Anonymous on Feb 11, 2012
0

sorry that was 5

Anonymous on Feb 11, 2012
2

Here's an easy way: E(H^2) = E(H)^2 + Var(H) = 2^2 + 1.
Remember that Var(N) for a binomially distributed N is p(H)*p(1-H)*N = N/4.
Here N = 4, so Var = 1.

DavidS on Apr 30, 2012
0

5

Me on May 12, 2014

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