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Q.
Total number of $9$ -digit numbers that are divisible by $5$ is equal to
Permutations and Combinations
Solution:
A number is divisible by 5 if it either ends with 5 or with zero.
(i) Total number ending with zero $=9 \cdot 10^{7}$
(ii) Total number ending with $5=9 \cdot 10^{7}$
Thus, total number of such numbers $=18 \cdot 10^{7}$