The measurement 28

The measurement 28.0 cm has three . To convert this to meters you need to divide 28.0 by 100 (because 1m = 100cm). The answer is 0.280 with the 0 at the far right being considered a significant figure because it comes to the right of the decimal point after non-zero digits.

I am assuming when you write 1000. meters you mean for the value to have four significant figures. To write this number with 4 sig figs it really should be written 1.000 x ##10^3##m. Some chem teachers would really frown on writing it as 1000. m to indicate four sig figs. (Did your teacher write it that way?) ;)

To convert from m to km you need to divide by 1000, so your answer will be 1. The correct way to write this to show 4 sig figs is: 1.000km