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| Math Central | Quandaries & Queries |
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Question from Paulo, a student: Hi , if i have to discover a keypad number of four digit , Which the closest combination of getting right?? i have this tips ---> i know the second and thirth number is odd . dont have the number 7 in any digit , Thanks !! |
Hi Paulo.
First digit is 0, 1, 2, 3, 5, 6, 9: seven choices,
Second digit is 1, 3, 5, 9: four choices,
Third digit is 1, 3, 5, 9: four choices,
Last digit is 0, 1, 3, 4, 5, 6, 7, 8, 9: nine choices.
They are independent of one another, so just multiply the possibilities together to find the number of four digit sequences that fit your specifications: 7 x 4 x 4 x 9.
Stephen La Rocque.>
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