SOLUTION: (i) Find how many different numbers can be formed using 4 of the digits 1, 2, 3, 4, 5, 6 and 7 if no digit is repeated. (iii) odd and less than 3000 ans 480

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Question 1069231: (i) Find how many different numbers can be formed using 4 of the digits 1, 2, 3, 4, 5, 6 and 7 if no digit is repeated.
(iii) odd and less than 3000




ans
480
Answer by ikleyn(52781) About Me  (Show Source):
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(i) Find how many different numbers can be formed using 4 of the digits 1, 2, 3, 4, 5, 6 and 7 if no digit is repeated.
(iii) odd and less than 3000
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(i)   Any of 7 digits in the first position (first counting from the left, which is "thousands" digit);

      Any of 6 remaining g digits in the next position;

      Any of 5 remaining g digits in the next position;

      Any of 4 remaining g digits in the next position.


      In all,  7*6*5*4 = 840 numbers.


(ii)  It is not clear to me if repeating is allowed in this case.