[tex] \text{To write a number with the least value using digits 1 through 9}\\ \text{and each digit only once. So we have total 9 digits.}\\ \\ \text{So for such number we must put the largest digit at unit place,}\\ \text{then the second largest digit on the tenth place, and then third}\\ \text{largest digit on the hundredth place and so on.} [/tex]
[tex] \text{so proceeding in this way we need to write the digits with 1 at}\\ \text{the leftmost position.}\\ \\ \text{thus the number with the least value using digits 1 through 9 with}\\ \text{each digit using once is: } [/tex] 123456789
