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Hint: Make 3 blank spaces of ‘Ones’, ‘Tens’, ‘Hundreds’ and start checking how many numbers can be placed without repeating.

Complete step-by-step answer:

A three digit number is to be formed from given 9 digits 1,2,3,4,5,6,7,8,9

$

\begin{array}{*{20}{c}}

\_&\_&\_

\end{array} \\

{\text{H T O}} \\

$

Now, there are 9 ways to fill ‘Ones’ place.

Since repetition is not allowed, so ‘Tens’ place can be filled by the remaining 8 digits.

So, ‘Tens’ place can be filled in 8 ways.

Similarly, to fill ‘Hundreds’ place, we have 7 digits remaining.

So ,’Hundreds’ places can be filled in 7 ways.

So, the required number of ways in which 3-digit numbers can be formed from the given digits is 9×8×7= 504

Note: The above problem can also be asked with repetition. In that case the answer would be 9×9×9= 729 as all the places can be filled with the same or different number i.e. all 9 digits.

Complete step-by-step answer:

A three digit number is to be formed from given 9 digits 1,2,3,4,5,6,7,8,9

$

\begin{array}{*{20}{c}}

\_&\_&\_

\end{array} \\

{\text{H T O}} \\

$

Now, there are 9 ways to fill ‘Ones’ place.

Since repetition is not allowed, so ‘Tens’ place can be filled by the remaining 8 digits.

So, ‘Tens’ place can be filled in 8 ways.

Similarly, to fill ‘Hundreds’ place, we have 7 digits remaining.

So ,’Hundreds’ places can be filled in 7 ways.

So, the required number of ways in which 3-digit numbers can be formed from the given digits is 9×8×7= 504

Note: The above problem can also be asked with repetition. In that case the answer would be 9×9×9= 729 as all the places can be filled with the same or different number i.e. all 9 digits.

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