Discussion

Explanation:

Let us label the digits of 5-digit number as 4 3 2 1.

The rightmost digits i.e., 1^st digit can be filled by either of 2 or 3 or 4 or 7 or 8, i.e., in 5 ways.

Now since repetition is not allowed, 2^nd digit can be filled by any of the 4 remaining numbers, i.e., in 4 ways.

Similarly, 3^rd digit can be filled by remaining 3 numbers in 3 ways.

and 4^th digit can be filled in 2 days.

⇒ Total number of such 5-digit numbers = 5 × 4 × 3 × 2 = 120.

Hence, 120.

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