How many four digit numbers can be formed using the digits {1, 3, 4, 5, 7,9}(repetition of digits is not allowed)?
Correct answer: A. 360
- A. 360
- B. 60
- C. 300
- D. 180
Explanation
There are 6 distinct digits and repetition is not allowed, so the four places can be filled in 6 x 5 x 4 x 3 = 360 ways. Since none of the digits is zero, there is no leading-place restriction. The likely trap is option d, 180, from incorrectly imposing a restriction on the first digit.
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