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How many 4-digit numbers have the second digit even and the fourth digit at least twice the second digit?

 Apr 29, 2022
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9 possibilities for the first and third digits, and if the second digit is 2, there are 6 possibilities for the last digit, and if the second digit is 4, there are 2 possibilities for the last digit.

 

So the answer is 9*9*(6 + 2) = 648.

 Apr 29, 2022

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