500
It depends on whether you are rounding to the nearest integer, nearest 10, nearest 50 etc.
Infinitely many, since between any two numbers, there are always additional numbers. The exact range of numbers that can be rounded to 3000 depend on how you are rounding - specifically, if you are rounding to the nearest integer, the nearest 10, the nearest 100, or the nearest 1000.
1000
Unfortunately integers ending in 0s are ambiguous. If 40300 is rounded to the nearest unit, there are five significant figures, if 40300 is rounded to the nearest ten, there are four significant figures and if 40300 is rounded to the nearest hundred, there are three significant figures.
88500
There are infinitely many such numbers.
0
500
800
21079000000 rounded to the nearest hundred thousand is 21079000000
There aren't any numbers that round to 350 to the nearest hundred.
98600
7464000 tons rounded to the nearest hundred thousand would be 7500000 metric tons.
All numbers can be rounded to the nearest ten.
An infinite number.
530