Three digits can't possibly add up to 900. The largest possible sum of 3 digits is (9 + 9 + 9) = 27.
900 of them.
There are 900 6-digit palindromes.
Assuming that 001, 080, etc are not allowed (that is a leading zero or two is not permitted), the smallest number with exactly three digits is 100. The largest number with exactly three digits is 999. So there are 999 - 100 + 1 = 900 numbers with exactly three digits.
There are 900 of them.
3 of them.
Yes
890
900
300, 600 and 900.
Three digits can't possibly add up to 900. The largest possible sum of 3 digits is (9 + 9 + 9) = 27.
850
450 or 900
144, 324, 576, 900
900 of them.
There are 900 6-digit palindromes.
There are 900 three-digit numbers.