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Problem Of The Week 42

with 4 comments


Let their be 7 special coins such that they are numbered from 1-7 on one side and blank on the other side. You toss all the 7 and let them fall and make your best guess as to which coin is 1, what is the probability that you are correct?

Written by Implex

October 3, 2008 at 4:20 pm

4 Responses

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  1. The best case scenario could be that they all fall in a row from 1to 7
    Probability
    4/32 = 1/8

    tyro

    October 3, 2008 at 5:09 pm

  2. we dont want the best case
    best case will be when one turns up 🙂

    we want the best guess

    outtimed

    October 3, 2008 at 5:11 pm

  3. There are total 8 cases
    Case 1 : When all the coins fall as blank.
    Case 2 : When one coin fall blank and rest 6 as numbered.
    Case 3 : When 2 coin fall blank and rest 5 as numbered.
    Case 4: When 3 coin fall blank and rest 4 as numbered.
    Case 5 : When 4 coin fall blank and rest 3 as numbered.
    Case 6: When 5 coin fall blank and rest 2 as numbered.
    Case 7: When 6 coin fall blank and rest 1 as numbered.
    Case 8: When all coin fall as numbered.

    Thus the probability will be 1/2 + 1/2[(1/2)^6+(1/2)^5*1/2*1/2+(1/2)^4*(1/2)^2*(1/3)+(1/2)^3*(1/2)^3*(1/4)+(1/2)^2*(1/2)^4*(1/5)+(1/2)*(1/2)^5*1/6]

    riya

    October 4, 2008 at 10:18 am

  4. rightly done riya !

    outtimed

    October 4, 2008 at 10:22 am


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