I'm posting one puzzle, riddle, math, or statistical problem a day. Try to answer each one and post your answers in the comments section. I'll post the answer the next day. Even if you have the same answer as someone else, feel free to put up your answer, too!
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?
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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40 pennies
ReplyDelete8 nickels
2 dimes
80 % probability that the dropped coin is a penny
Donnie scharm@ureach.com
hmmmm.... I got 90%, because of 45 pennies, 1 quarter, 2 nickels and 2 dimes.
ReplyDeleteWhich means, between the two of you, you figured out the two different ways you can get $1 out of 50 coins.
ReplyDeleteSince 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%.