Answer: 120
Step-by-step explanation:
The total number of digits from 1 to 9 = 10
The number of digits from less than 5 (0,1,2,3,4)=5
Since repetition is not allowed so we use Permutations , then the number of 3-digit different codes will be formed :-
[tex]^5P_3=\dfrac{5!}{(5-3)!}=\dfrac{5\times4\times3\times2!}{2!}=5\times4\times3=60[/tex]
The number of digits from greater than 4 (5,6,7,8,9)=5
Similarly, Number of 3-digit different codes will be formed :-
[tex]^5P_3=60[/tex]
Hence, the required number of 3-digit different codes = 60+60=120
