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Explanation:

The total number of 8-digit landline telephone numbers that can be formed having at least one of their digits repeated = The total number of 8-digit landline numbers – The number of 8-digit landline numbers in which no digit is repeated.

The total number of 8-digit landline numbers = 108

The number of 8-digit landline numbers in which no digit is repeated = 10!/2

∴ Number of required landline numbers = 98185600

Hence, option (a).

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