What is the largest 8 digit number?
(a). 888999
(b). 99999999
(c). 999999
(d). 8999999

Hint: The largest 8 digit number is formed by the largest digit among the digits 0 to 9. An addition of 1 to it results in the smallest 9 digit number.
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Complete Step-by-Step solution:
An 8 digit number begins with a crores place in the crores period. For example, 8,00,00,000 is a 8-digit number.
The largest 8 digit number means that the number should have exactly 8 digits and any other 8 digit number is smaller than or equal to this number but never greater than this number.
We have the digits from 0 to 9 to fill in each of the places such that the final number is the greatest 8 digit number.
In the crores place, we fill the greatest digit among the digits from 0 to 9, which is 9. Hence, we have:
9 _ _ _ _ _ _ _
In the ten lakh’s place, we again fill the greatest digit among the digits from 0 to 9, which is again 9. Hence, we have:
9 9 _ _ _ _ _ _
In the lakh’s place, we again fill the greatest digit 9. Then, we have:
9 9 9 _ _ _ _ _
Hence, it follows a pattern and similarly, all the digits are chosen to be 9. Hence, the number is given as follows:
9 9 9 9 9 9 9 9
Hence, the greatest 8-digit number is 99999999.
Hence, the correct answer is option (b).

Note: The option (c) resembles very well the correct answer, hence, you may choose it by mistake but note that it is a 6 digit number and not an 8 digit number. Hence, the option (c) is wrong.