There aren't any numbers that round to 350 to the nearest hundred.
Ten to the nearest ten.
350 to 449 -- 100 numbers
10 of them.
Infinitely many. There are infinitely many numbers between any two numbers.
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.
3550 to 3649 -- 100 numbers
There are infinitely many numbers, and their ranges will depend on the level to which the numbers are rounded.To the nearest 600: [300, 900)To the nearest 300: [450. 750)To the nearest 10: [595, 605)To the nearest 5: [597.5, 602.5) and so on.
Infinitely many. There are infinitely many numbers between any two numbers. So, for example, cosidering only the numbers that round up, there are an infinitely many numbers between 149.999 and 150, all of which would round to 150. And there are another infinity between 149.5 and 149.999 which, to the nearest unit would round to 150. If you are rounding to the nearest 10, all the numbers between 145 and 150 would also round to 150. In all cases you must also consider the numbers that are rounded down to 150.
There are an infinite amount of numbers that round to 800. This is because of the infinite amount of decimals and also that you have different rounding values, like to the nearest 100 or the nearest 10 etc., that you could use.
this is the answer you require: [550,650) i.e all numbers from 550 including 550, till 650 excluding 650. If you want to know the no. of integers, it is: 100. If you want to know the no. of real numbers, we can't count them i.e. infinite no. of numbers!