How many 4-digit numbers can be made using the digits 0 to 7 without repetition?
Explanation:
Here 0 cannot come thousand’s place, hence
Number of ways of filling thousand’s place = 7 ways (digits 1 to 7)
Number of ways of filling hundred’s place = 7 ways (now digit 0 is also available)
Number of ways of filling ten’s place = 6 ways
Number of ways of filling unit’s place = 5 ways
∴ Total 4-digit numbers = 7 × 7 × 6 × 5 = 1470.
Hence, 1470.
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