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gretchen knows the combination to a bank vault is two letters followed by 2 numbers.

 

A) what is the probability that gretchen guesses the combination on her frist attempt

 

 

B) suppose she knows the combination starts with the letter M

what is the probability she guesses the comination on her frist attempt.

cheifraidhunter  Jun 8, 2017
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 #1
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A)  Allowing for repeated letters/numbers  we have   (26)^2 * (10)^2  =  67,600  possible codes

So....the chance of guessing correctly the first time is    1 /67,600 ≈ 0.0000148  =  .00148%

 

B)  With M being  the first letter, there are  26 * 10^2  codes  =  2600 possible codes

The probability of a correct guess  on the first attempt  =  1/2600  ≈ 0.0003846  = .03846 %

 

 

cool cool cool

CPhill  Jun 8, 2017
 #2
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+1

thanks matecool

cheifraidhunter  Jun 9, 2017

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