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HOW MANY 3-DIGIT EVEN NUMBERS CAN BE MADE USING THE DIGITS 1,2,3,4,5,6,7. IF NO DIGITS ARE REPEATED?
Since the last digit is even, the number pattern is 
1)odd, odd, even
2)odd, even, even
3)even, odd, even
4)even, even, even

1)The number of ways of choosing first digit is 4.
   The number of ways of choosing second digit is 3.
   The number of ways of choosing third digit is 3.
So number of ways = 4 x 3 x 3
                              = 36
2)The number of ways of choosing first digit is 4.
   The number of ways of choosing second digit is 3.
   The number of ways of choosing third digit is 2.
So number of ways = 4 x 3 x 2.
                              = 24.
3)Number of ways  = 3 x 4 x 2
                              =24
4)Number of ways = 3 x 2 x 1 = 6

Total = 36 + 24 + 24 + 6 = 90


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