Tuesday, February 02, 2010

How Did You Know There Were Fifty Coins?

Mary had a coin purse with fifty coins, totaling exactly $1.00.  Unfortunately, while counting her change, she dropped one coin.  What is the probability that it was a penny?


  1. 40 pennies
    8 nickels
    2 dimes
    80 % probability that the dropped coin is a penny

    Donnie scharm@ureach.com

  2. hmmmm.... I got 90%, because of 45 pennies, 1 quarter, 2 nickels and 2 dimes.

  3. Which means, between the two of you, you figured out the two different ways you can get $1 out of 50 coins.

    Since we have no indication of which of the two Mary had, the chances are even it was either. That means the probability of the coin being a penny is 85%.


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