RY G.

asked • 06/09/15

A thief steals an ATM card and must randomly guess the correct 4 digit pass code from a 9-Key key pad. Repetition Is allowed. What is the probability of a corre

I don't know what formula to use for this question 1/9 to the 9th power is way to large of a number.n where did i go wrong?

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Nathan B. answered • 06/09/15

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The trick is that you need only four button presses. Since the thief has a 1/9 of a chance to get any button correct, the equation is:
1/9 * 1/9 * 1/9 * 1/9, which becomes 1/6561
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David W.

It seems unusual that an ATM would have a 9-digit key pad rather than a 10-digit key pad (allowing the use of 0 also), but then the probability would be 1/1000 or simply, "the pass code is one of the numbers between 0000 and 9999," which would make this problem a lot more understandable.
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06/09/15

David W.

Oops, typo, I meant 1/10000.
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06/09/15

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