The greatest 8-digit number is:
(a) 99999999
(b) 10000000
(c) 9999999
(d) 88888888

Hint: We will check every option step by step to get the greatest 8-digit number. Greatest 'n' digits number is a number with all of its digits equal to 9.

Complete step-by-step answer:
A 8-digit number is a number that has 8 digits where the first digit must be 1 or greater.
Let’s start with option (a), 9 is the greatest digit and here the number of digits is 8 and all the digits are 9. So yes 99999999 is the greatest 8-digit number. This option is right as it is the greatest 8-digit number.
Let’s check option (b), 1 is the greatest digit in this number and here the number of digits is 8 and 1 is followed by 7 zeros. So 10000000 is the smallest 8-digit number. This option is wrong as it is the smallest 8-digit number.
Now let’s check option (c), 9 is the greatest digit in this number and here the number of digits is 7 and all the digits are 9. So this option is wrong as the digits are 7.
Now we see option (d), here the number of digits is 8 and all the digits is 8. But it cannot be the greatest because 9 is a bigger digit than 8 and thus this option is also wrong.
So 99999999 is the greatest 8-digit number and hence the correct answer is option (a).

Note: We can commit a mistake in a hurry by selecting option (c) as the answer but we have to be careful here as the number of digits is 7. We may also get confused with option (b) but it is the smallest 8-digit number.