199
555
2722
0
The smallest number that is 600 when rounded to the nearest hundred is 550. The largest number that is 600 when rounded to the nearest hundred is 649.
2400
5600
The number would be 2666. 6 is repeated 3 times. Rounded to the nearest hundred is 2700 and rounded to the nearest thousand is 3000.
The mystery number is 155. When rounded to the nearest hundred, it rounds to 200. The sum of its digits is 1+5+5=11 which is greater than 10, so we must adjust the digit in the hundreds place. When rounded to the nearest ten, 155 rounds to 160, which has digits summing up to 1+6+0=7.
If you're talking about whole numbers, then it's 6,049 .If you're talking about any number, including decimals and fractions, then there's no "greatest possible" one.
555
555
600
2722
-12
3200
0
0