![How many 3 - digit numbers can be formed from the digits 1, 2, 3, 4 and 5 assuming that repetition of the digits is not allowed? How many 3 - digit numbers can be formed from the digits 1, 2, 3, 4 and 5 assuming that repetition of the digits is not allowed?](https://i.ytimg.com/vi/UTqIB3B5ONA/maxresdefault.jpg)
How many 3 - digit numbers can be formed from the digits 1, 2, 3, 4 and 5 assuming that repetition of the digits is not allowed?
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How many 4-digit numbers can be formed by using the digits 1 to 9 if repetition of digits is not allowed?
![How many 4-digit numbers can be formed by using the digits 1 to 9 if repetition of digits is not allowed? How many 4-digit numbers can be formed by using the digits 1 to 9 if repetition of digits is not allowed?](https://d10lpgp6xz60nq.cloudfront.net/web-thumb/437_web.png)
How many 4-digit numbers can be formed by using the digits 1 to 9 if repetition of digits is not allowed?
![probability - Best strategy to pick a lock which opens if at least two of its three decimal digit wheels are dialed correctly? - Mathematics Stack Exchange probability - Best strategy to pick a lock which opens if at least two of its three decimal digit wheels are dialed correctly? - Mathematics Stack Exchange](https://i.stack.imgur.com/YGl7R.png)