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# I do not understand what does it mean by smudges?

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I need only b​)

Thanks in advance for the help

Jun 20, 2022

#1
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what does it mean by smudges?

It's a method of hacking a passcode by examining the screen for the smudges left on the screen above the digits by oily fingers.  The idea is that when the legitimate user taps in the passcode, the digits he touched will be smudged.  So that reveals which digits are in the passcode, therefore narrowing down the possible combinations.

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Jun 20, 2022
#2
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it doesn't make sense to me. Does it mean that all digits are different and no digit can be the same?

Guest Jun 20, 2022
#4
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By the conditions of the problem, yes.  It says that four digits were used in the four digit passcode.

Guest Jun 20, 2022
#3
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In the question, the word "smudges" is referring to a mark.

The question is trying to ask: If you knew that 4 distinct numbers were used in the 4 digit passcode, how many passcodes would be possible?

Jun 20, 2022