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A cent or more? (Posted on 2017-05-01) Difficulty: 2 of 5
Mary had exactly 21 coins in her purse, total value of a round dollar.
While counting her money, she dropped a coin.

Evaluate the probability it was a penny.

No Solution Yet Submitted by Ady TZIDON    
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Coin distribution Comment 2 of 2 |
From Charlie's post it appears we need to have some information about the distribution of the coins Mary has.  The most recent data I could find is from https://en.wikipedia.org/wiki/United_States_Mint_coin_production

The most recent entry in the chart is distribution for 2015:
Pennies: 9,365,300,000 
Nickels: 1,599,600,000
Dimes: 3,041,010,000
Quarters: 2,990,820,000
Half-Dollars: 4,600,000

Charlie's fourth set (0 half-dollar, 2 quarters, 3 dimes, 1 nickel, 15 pennies) is closest to the 2015 Mint distribution.  So if the Mint distribution is taken as our basis of coin distribution then the probability Mary dropped a penny is likely to be close to 15/21.

  Posted by Brian Smith on 2017-05-01 10:25:44
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