| Topic Name: |
Interview Question - ideas? |
| Message Name: |
Game |
| Date Posted: |
02/15/2006 |
| In Reply To: |
I just had a research analyst interview where I was asked a tough question. Suppose you have a coin that's not fair - 70% will be heads and 30% tails. How could you change these probabilities to 50% heads and 50% tails. I think interviewer wanted to know how to build a system and how to adjust for this bias. I suggested making 2 of the heads tails but was told 'how would you know which to change'. Any ideas? |
| Message: |
You need two flips of this coin for each "fair" test of a coin. Here is how you proceed: If your first flip is heads, flip again. If this is again heads then the result of the "fair" test is approximately heads because
.7 * .7 = .49 = almost = .5
The other possible flips are
HT, TH, TT
which have probabilities (on the unfair coin)
.21, .21 and .09 (sum to .51)
(assuming the flips are independent).
Any of these combination of two flips are considered "tails" on the fair test.
So you have almost a fair coin. Wow, not bad. I had never seen it before.
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